I. The UK's present situation in view of "Justice/Home Affairs" policies
1. Historical Reminder
The UK took an active part in the first steps towards cooperation in the area of security and justice in the European area. This approach was completed in 1975 via the creation of the TREVI group 
which took the shape of an intergovernmental network of Home Affairs and Justice Ministers from the 12 Member States at that time, outside of the framework of the European institutions.
The UK also took part in cooperation that the Member States were able to implement via the conventions of the Council of Europe 
and it concluded bilateral agreements in various areas. It also joined the Naples convention for mutual assistance between customs and excise administrations 
The UK also took a decisive part in the development of judicial cooperation in civil matters that was also intergovernmental in form. Here we think in particular of the 1968 Brussels Convention on jurisdiction and the enforcement of judgments in civil and trade matters which it joined in 1978 
and the 1980 Rome Convention on the law applicable to contractual obligations 
However the British stood back from the Schengen Agreements concluded in 1985 between the five Member States (Belgium, France, Luxembourg, Netherlands and West Germany) which chose to lift the internal borders dividing them.
With the Maastricht Treaty (1992) which founded the European Union, issues pertaining to justice and security were included in the community's institutional framework. However the new so-called "Justice and Home Affairs" (JHA) policy, became part of a specific intergovernmental framework, "the third pillar". Although by doing this the Member States acknowledged that these matters might be of common interest, they did however take care to reserve a right to veto, via the unanimity rule, which sufficed to brandish as a threat to achieve concessions in line with their national interests. The UK was happy with this.
The Amsterdam Treaty (1997), which set the ambitious goal of turning the European Union into an area of "freedom, security and justice", modified the landscape quite significantly. Firstly, this was because it integrated the Schengen acquis
(which apart from the agreements per se, include the 1990 application convention). Then because it incorporated, in the third part of the treaty on the European Communities (TEC), Title IV "visas, asylum, immigration and other policies linked to the free movement of people," covering policies that were transferred from the third intergovernmental pillar to the first community pillar. In effect this meant the application of the qualified majority rule in the Council, thereby depriving the Member States of their right to veto. In addition to this the EU was now able to conclude international agreements with third countries, thereby affecting police and judicial cooperation in criminal matters. Of note are the agreements that were made by the EU in the 2000's with the USA, Canada and Australia regarding the transfer of air passenger data ("PNR"- Passenger Name Record - data).
In this context the UK achieved a special status via three protocols regarding the new title in the treaty that was subject to the community pillar. One protocol exempted the UK from the measures taken in virtue of title IV, unless it decided to opt-in regarding specific measures 
. For the UK this meant guaranteeing that its national interests would be effectively protected, notably regarding the protection of specific features of its legal system. In real terms the opt-in entails notifying the Council of the intention to take part in the measure in question within three months of the submission of the proposal. If a decision is prevented because of the UK (or Ireland) the Council can adopt the measure which would then not apply to the former. Notification of the opt-in can also occur after the adoption of the measure in question. The UK, for example, chose to opt-in to six legislative measures in the "asylum package" which were adopted in 1999 and 2005 
A second protocol enables the introduction of a mechanism that is specific to the UK (and to Ireland) regarding its participation in Schengen 
. The country is not therefore tied by all of the Schengen acquis
. The request made to the Council has to be accepted by the latter unanimously. In this way it has participated since 2000 
in the Schengen acquis
in terms of police and judicial cooperation in criminal matters, the fight to counter drug trafficking and the Schengen Information System (SIS). This obliges it to participate in all of the initiatives and proposals regarding these areas. However it is not part of any of the measures comprising the development of the Schengen acquis
, in which it effectively has no participation. Since it wanted no part in the measures regarding border (and visas) controls the UK was unable therefore to participate in the adoption and application of the regulation establishing the agency FRONTEX 
2. The new exemption scheme after the Lisbon Treaty
The Lisbon Treaty significantly modified the legal framework in which issues relative to the area of freedom, security and justice are adopted 
. By removing the existing structure of "pillars", it has subjected nearly all new measures to the qualified majority rule in the Council, whereas before they were adopted unanimously under the former third pillar. Moreover nearly all of these measures now have to be adopted in co-decision with the European Parliament. The exceptions involve issues deemed sensitive by the Member States: the creation of a European Public Prosecutor's Office, (article 86 TFEU), family law (article 81 TFEU), operational police cooperation (article 89 TFEU), as well as measures pertaining to passports, identity documents, and residence permits (article 77 TFEU). The transfer over from unanimity to the qualified majority of the Council, regarding police and judicial cooperation measures deprived the Member States of the right to veto, and therefore, of their capacity to influence the texts and steer them according to their national interests. This is why the UK and Ireland negotiated amended protocols granting them the right to decide to participate or not in terms of any legislation involving the areas of justice and home affairs.
Under the Amsterdam Treaty the British opt-in enabled the UK (and Ireland) to decide to participate or not in the proposals for European legislation regarding asylum, immigration and border control, as well as civil judicial cooperation and family affairs. This opt-in compensated for the end of the unanimity rule at the Council regarding issues that had been reorganised under the community pillar. If the UK uses its opt-in right but blocks the decision-making process the Council can decide to adopt the measure without the UK, which will not be applicable to the latter. The UK (and Ireland) can also decide to opt-in at any time after the adoption of the measure by notifying the Commission and the Council that it wants to do so. However the 1997 protocol did not specify whether the UK was automatically bound by an ulterior modification of an act in which it takes part, which causes legal instability 
In the new post-Lisbon Treaty situation, which abolished the pillar structure, protocol 21 extended the specific regime that the British enjoyed to all issues pertaining to the area of freedom, security and justice. This meant that police and judicial cooperation in criminal matters were covered by the system of exemptions. However, since until that date police and judicial cooperation had been subject to the unanimity rule, it was now possible for the UK to oppose them. The consequences of the UK's refusal to be bound by a modification of an act in which it was participating were clarified. Although non-participation makes the application of the measure "impracticable by the Member States and the Union" the Council (by a qualified majority) can force the UK to relinquish its participation in the measure in its entirety. The Council (still by the qualified majority) can also decide that the UK has to bear, if necessary, the direct financial consequences that result "necessarily and inevitably" from the end of its participation in the existing measure. For example refusal to take part in an updated version of the Schengen Information System would lead to a modification of the system 
Moreover, pursuant to article 10 of the protocol 36 the UK had to decide by 31st May 2014 whether it wanted to continue to be bound by all of the measures in the area of police and judicial cooperation in criminal matters adopted before the Lisbon Treaty entered into force, or on the contrary, whether it wanted to opt-out completely of all of them. Protocol 36 also opened allowed the UK to join in individual measures. On 24th July 2013, following votes in both houses of parliament, the country decided to opt-out from all of the measures in question. The government did however say that it wanted to re-integrate a smaller number of measures that appeared to provide the British police and its security agencies real and vital support. In November 2014 it notified the Council that Britain wanted to take part in 35 cooperation measures that matched its national interests including Europol, the sharing of information with countries in the Schengen area and the European Arrest Warrant. The possibility of opting out also enabled the UK to limit - in its particularly case, the Court of Justice's competence to the JHA measures taken prior to the Lisbon Treaty and in which it takes part.
Protocol 19 confirmed that the UK could request participation in all or part of the measures under the Schengen acquis
at any time it wanted. It might also choose to take part or not in the development of the Schengen acquis
in which it participates. However an almost identical measure to that provided for by the protocol on the area of freedom, security and justice was introduced in the event of a refusal.
Protocol 30 covered the specific elements demanded by the UK (and Poland) regarding the application of the EU's Charter of Fundamental Rights. It indicates that the Charter does not extend the Court of Justice's capacity or that of a British jurisdiction to deem that the laws and regulations or national administrative practices are in contradiction with the fundamental principles reiterated in the Charter.
II. Remain or leave: a derogatory system to protect
1. Remaining in the European Union: the opt-in and the February 2016 arrangement
In the event of the UK deciding to remain in the Union on 23rd June, the derogatory regime that resulted from the Lisbon Treaty and the decisions taken by the British authorities on its basis would continue to apply. In addition to this we might add the measures resulting from the arrangement made for the UK during the meeting of the heads of State and government on 18th and 19th February 2016, which involve the implementation of the principle of free movement 
. These measures comprise the political commitments of the European Council and do not involve the revision of the treaties. However their application would suppose prior modifications to secondary laws as required. The application of the co-decision procedure will enable the European Parliament to assert its point of view regarding the arrangement. Moreover it will suppose a certain time span before the measures can effectively enter into force.
Basically the arrangement acknowledges that it is legitimate to take an exceptional situation into account. It is therefore possible to provide at Union and national level measures that help stem flows of workers when these are so great that they have a negative effect both the Member States of origin and also destination.
In addition to this, limits can be set on the right to free movement for social and economic reasons, and also for reasons pertaining to public order, security or public health. Hence if imperious reasons of general interest justify the situation, the free movement of people can be restricted by measures in line with the goal that is legitimately being pursued.
The arrangement includes a warning mechanism and an emergency brake designed to rise to the challenge of an (exceptional) influx - and for an extended period - of workers from other Member States. As a result a Member State will, after an assessment, and on the proposal of the Commission, be able to restrict access to non-contributory work associated benefits. However this restriction must be gradual and progressive access must be accommodated so that the worker can receive all benefits after a period of four years. This type of authorisation will be limited to a period of 7 years. The European Commission admits in the arrangement that in view of its situation the UK can already activate this mechanism.
The arrangement also grants that the Member States can index the family allowance that is to be sent to children back in the country of origin according to conditions that prevail in the Member State where the child is living. But this will only apply to workers who arrive after the entry into force of the arrangement. After 2020 the measure will be become standard.
The arrangement also provides measures to counter marriages of convenience for citizens from a Member State with people from extra-community States who are trying to guarantee their entry into the Union, and to prevent the entry of certain people from other Member States who are a threat to public order or security. Finally, transitory measures will be taken when future enlargements occur in the Union in order to limit the movement of people from the new Member States. The new measures will be integrated into the treaties when they are next revised.
Considerations in the arrangement regarding the scope of the principle "ever closer Union" will simply strengthen the UK's position based on the opt-in/opt-in in terms of the JHA policies. Indeed the arrangement states that the UK will no longer be obliged to take part in greater political Union. Moreover, the agreement recognises, in this instance that the reference to "ever closer union between the peoples of Europe" does not comprise a legal base to extend the scope of the measures contained in the treaties and the Union's secondary laws, and in no way can it be used to support an extensive interpretation of the Union's competences or the powers of its institutions.
The reference to "ever closer union" cannot prevent Member States "from taking other paths of integration" either, nor can it force all of the Member States to aspire to a common future. Hence the idea of a two-tiered Europe is now official and this will allow the UK to assert its singularity particularly in the definition and undertaking of JHA policies.
In addition to this the UK will also be able to try to block proposals in this area that seem contrary to its national interests by using as a support the commitments of the European Council regarding national parliaments under the subsidiarity principle. In the event of the motivated opinions of the national parliaments regarding the non-respect of the subsidiarity principle by a draft EU legislative act represent more than 55% of the votes attributed to the national parliaments the presidency of the Council will enter the question on the agenda, so that these motivated opinions and the lessons to be learnt from this can be the focus of in-depth debate. Following this debate the Member States' representatives will finalise the assessment of the draft bill in question or they will modify it to take on board the concerns expressed in the motivated opinions.
2. Exit of the UK: towards a sectoral approach protecting British singularity?
Various options are possible to manage the situation that would arise if the UK were to quit the European Union 
. We can however consider that the country will necessarily have to come to an agreement with the Union, particularly regarding settlement of issues relative to the area of freedom, security and justice. This is firstly because British citizens living in the Member States will lose the rights attached to European citizenship. Then because the UK said it was interested in cooperation measures that it wanted to re-integrate in November 2014 after its opt-out of July 2013, notably via Europol, the sharing of information under Schengen and the European Arrest Warrant. Reciprocally the Member States would have an interest in such an agreement for similar reasons: on the one hand the situation of their own citizens living in the UK would have to be settled; on the other British participation in police and judicial cooperation in criminal matters is a condition for the measures to be totally effective 
. However, whatever the shape the agreement takes, the British situation, now outside of the Union would be typified by the application of the measures set by the EU without the UK being able to influence their content.
Some measures might be provided for in the withdrawal agreement planned by article 50-2 of the Treaty on European Union (TEU). In this context the UK might try to promote a sectoral approach to JHA issues enabling it to include in the agreement the choices that itself made as a member of the Union in virtue of the opt-in or recover the benefit, in part or entirely, of the measures in the arrangement that would become null and void following its decision to quit the Union. If in principle the Member States might themselves find an interest in a compromise like this, several impediments can be identified that would have to be overcome if agreement were to be reached. The Union would be reticent about an overly sectoral approach that would lead to simply giving a country that had decided to leave the Union the advantages it seeks, without making it bear the constraints shared by the Member States within the Union; then the Union would want to ensure the protection of its decision making capacity and to provide for specific measures in the agreement to guarantee the legal control of the respect by the UK of its commitments. From a procedural point of view the terms of the agreement would obligatorily have to be broadly approved. Its "guidelines" would in effect be the focus of a consensus within the European Council; the decision to conclude the agreement would itself be taken by the qualified majority of the Council with the approval of the European Parliament; an opinion on the part of the Court of Justice might also be required regarding its compatibility with the treaties (article 218§11 TFEU) 
. Moreover in virtue of article 50 TEU, the treaties would in principle cease to be applicable in the UK as of the date of the entry into force of the withdrawal agreement or 2 years after the notification of its decision to withdraw, except, if in agreement with the UK, the European Council unanimously agreed to extend this deadline. The procedure might therefore open the way to long discussions during which time the treaties would continue to apply to the UK.
The sectoral approach to JHA questions might arise if relations between the UK and the EU were to follow the "Swiss Path". Following Switzerland's refusal on 6th December 1992 to ratify the agreement on the European Economic Area by referendum, bilateral agreements were negotiated to prevent Switzerland becoming isolated on the continent. Several of these agreements involve issues regarding the area of freedom, security and justice: free movement of people, Schengen; Dublin; Europol; Eurojust; the European Asylum Support Office 
. Again we should not underestimate the obstacles that this kind of solution might come up against. Of course these bilateral agreements are based on traditional international law. The EU's partner is not in principle bound by the decisions of the Court of Justice. In practice it finds itself obliged to apply the Union's secondary law (directives and regulations) without being able to participate in the drafting of these 
. Moreover the European Union said in December 2010 that it wanted to review the framework of its relations with Switzerland, which it deems extremely complicated. In May 2014 it decided to start negotiations in view of an agreement that was due to grant the European Commission a monitoring role and a judicial supervisory role to the Court of Justice. Although we cannot foresee the result of the negotiations that the Union would be called to undertake with the UK, we see however via the "Swiss precedent" what its line of conduct might be.
If we consider the main areas that might be involved by one (or several) agreements with the UK we can imagine that the free movement of people would be the focus of discussions. Indeed, it was one of the main lines of request made by the British Prime Minister and the arrangement of February 2016. It would be a priority to settle the situation of British citizens established in the EU and likewise that of the Union's citizens living in the UK. Again the Swiss example offers a few ideas. The agreement of 21st June 1999 grants Swiss citizens the right to choose their place of work and residence freely in the States taking part. But to do this they have to have a valid work contract, undertake an independent activity and - if they do not have a lucrative business - have adequate financial means and health insurance. The UK could try to ensure the continuity of the concessions that it achieved in the arrangement. The Swiss framework again provides enlightenment: since on 9th February 2014 Swiss citizens accepted the people's initiative "against mass immigration", further constitutional measures require that immigration be managed with ceilings and contingents taking on board the country's economic interests. They rule out the conclusion of agreements that are incompatible with the introduction of contingents for immigrants. We might also note that the free movement of people went together with additional measures against undercutting wages and social dumping. However the Swiss position goes against the principles that the EU itself tries to promote in terms of free movement 
The UK's relations with the Schengen Area should be settled by the withdrawal agreement or by a sectoral agreement. It would not be the first non-EU member country to join the Schengen Area since Iceland, Switzerland, Norway and Liechtenstein are all in the same situation. Conversely four Member States - Bulgaria, Cyprus, Croatia and Romania - are not part of it. However the UK would try to retain the specific status that it enjoys at present. From its point of view the agreement should therefore only target a part of the acquis regarding police and judicial cooperation in criminal matters, the fight to counter drug trafficking and the Schengen Information System (SIS).
Regarding asylum law the British position comprises assessing each of the laws according to their own merits 
. Hence it subscribed to a "first asylum package" but not to the new "package" including the new reception conditions, the qualifications for international protection and asylum procedures. However it decided to opt for the EURODAC and the Dublin regulations which enable the registration of asylum seekers (fingerprinting) and the definition of a single State responsible for the processing of the asylum request. The real cooperation mechanisms, for example the European Asylum Support Office, would be selected under a new agreement. However the UK would not take part in the return measures 
. Likewise they would remain reticent about measures pertaining to the legal migration of third country citizens to the Union, since the dominant criteria are that national control procedures are better for national interests and in terms of taking on board the needs of the British economy 
The UK cooperates with EUROPOL under the Council Decision of 2009. During the review of competences, the agency's managers stressed that participation in EUROPOL had been beneficial for the country. Immigration Minister James Brokenshire, advocated opting for the new EUROPOL regulation 
, on condition that it does not have any executive powers over the national agencies, or that it can launch investigations or benefit from data sharing that would be incompatible with national security 
. We might then think that the UK wants - if it does exit the Union - to maintain cooperation on the same basis under this framework, for example with an agreement settled directly with EUROPOL 
In terms of judicial cooperation in criminal matters the UK takes part in EUROJUST. It will probably not participate in the future European Public Prosecutors' Office if this ever came to be. The EU Act of 2011 specifies that the British government cannot accept participation in a structure like this without a referendum and an Act of Parliament. The British government has therefore chosen not to opt for the reform of EUROJUST, notably considering its interaction with the project for the European Public Prosecutors' Office. In all likelihood the competences of the European Prosecutors' Office, which would initially be limited to protecting the Union's financial interests, would not be of interest to a country that had quit the EU 
. On the contrary the UK might find an interest in maintaining the principle of mutual acknowledgement of the decisions of justice, which has governed judicial cooperation in the Union since the Tampere Programme of 1999. However the competence review noted analyses stressing that the goal pursued might also be achieved via intergovernmental agreements or non-legislative means 
. These two paths might therefore be privileged to the detriment of a global approach under the framework of the agreement with the European Union. The possibility opened up by the Lisbon Treaty for harmonisation in terms of criminal matters (article 82 TFEU) has not raised a great deal of interest in the UK, which has deemed that in most cases its legislation already meets with the minimum standards set by the European Union 
. It also selected European measures to harmonise criminal procedures 
. The same should apply in the context of negotiations over a "post-Brexit" agreement. The UK has also benefited from international multilateral agreements made in this area by the EU. However the British government asserts in the competence review that the goals might be achieved in particular via bilateral agreements.
To date in the area of judicial civil cooperation the UK has opted-in according to the assessment of its national interests. In practice it has adopted most of the legislative proposals within the three months of their publication. It has however reserved the possibility of waiting for the adoption of the measure in question, for example regarding the "Rome I" regulation, because of the difficulties caused for the UK by the initial proposal. We also note in the competence review that care has been taken to protect the integrity of the British legal system and of constructive relations with international organisations like The Hague Conference on International Private Law 
. Both of these paths might inspire the UK in a post-Brexit scenario.
Finally in terms of fundamental rights the issue of the European Charter might appear to be finally resolved, since in all likelihood, this only applies if the Member States "implement the Union law". However we might consider that under an agreement made with the EU, the UK would be called to apply at least part of the Union's law even if it did not participate in drafting it. But the British position would still be to protect its domestic law from interference by the Charter. Finally, based on a long tradition, the UK can rely on sound guarantees in this area. As a member of the UN, it takes part in the organisation's various instruments and conventions in terms of Human Rights and the conventions of the International Labour Organisation. As a member of the Council of Europe it is also bound by the European Convention of Human Rights 
, even though the controversy caused by some decisions taken by the European Court of Human Rights in its regard spring to mind. 
: The TREVI group was the acronym for Terrorism, Radicalism, Extremism and International Violence. It formed on 1st July 1975 in an informal framework. It brought together the Home Affairs and Justice Ministers of 9 EEC Member States as well as of two associate States.
: For example the European Convention for mutual legal assistance in criminal matters of 20th April 1959 and the European Extradition Convention of 13th December 1957.
: Convention of 7th September 1967.
: Convention of 27th September 1968.
: Convention of 19th June 1980.
: Protocol n° 4 on the UK and Ireland's position.
: i.e. the "Dublin II" (2003/43/CE) regulation, the "Eurodac" (2000/2725/CE) regulation, the "Temporary Protection"(2001/55/CE) directive, the "Reception Conditions" (2003/9/CE) directive, the "Qualifications" (2004/83/CE) directive and the "Procedures" directive (2005/85/CE).
: Protocol n° 2 integrating the Schengen acquis under European Union.
: Decision 2000/365/CE 29th May 2000.
: Court of Justice, 18th December 2007, UK c. Council, aff. C-77/05.
: Cf. Yves Doutriaux and Christian Lequesne, Les institutions de l'Union européenne après la crise de l'euro, La Documentation Française, 2013.
: Cf. François-Xavier Priollaud and David Siritzky, Le traité de Lisbonne, La Documentation Française, 2008.
: If on the contrary the UK did leave the EU, the arrangement would become null and void.
: Cf. Jean-Claude Piris: Brexit or Britin: will it really be colder on the outside? European Issue 369, Robert Schuman Foundation, 26 October 2015.
: Cf. As expressed by the Director of Europol Rob Wainwright, who deems that an exit by the UK might weaken police cooperation and transnational investigations in Europe, Wall Street Journal, 24th February 2016. The same observation might be made regarding the European Arrest Warrant.
: Cf Jean-Claude Piris, op. cit.
: Cf. Federal Department for Foreign Affairs: The Bilateral Agreement Switzerland-European Union, edition 2015.
: Cf. Review of the balance of competences between the United Kingdom and the European Union - Asylum & Non-EU Migration
: It did not opt for the European Parliament and Council's "Return"2008/115/CE directive dated 16th December 2008 regarding standards and common procedures applicable in the Member States to the return of citizens from third countries who are in an illegal situation.
: Cf note 21
: European Parliament and Council Regulation (EU) 2016/794 11th May 2016 on the European Union's Agency for Repressive Services Cooperation (Europol) thereby replacing and repealing the Council's decisions 2009/371/JAI, 2009/934/JAI, 2009/935/JAI, 2009/936/JAI & 2009/968/JAI.
: Cf. Review of the balance of competences between the United Kingdom and the European Union - Police and criminal justice.
: Cf. for example, the agreement of 24th September 2004 between Switzerland and EUROPOL.
: The issue might be set differently if the European Council one day decided to extend the European Public Prosecutors Office's competences to the fight to counter cross-border crime as enabled in the Treaty (article 86 TFEU). However even this might not lift the UK's reservations of principle.
: Op cit.
: The UK chose to opt in to directives on human trafficking, sexual exploitation of children and attacks on information systems.. However it did not opt in to the directive on counterfeiting, put forward by the European Commission in February 2013.
: For example the UK chose to opt for the directive on access to legal advice in criminal proceedings.
: Cf. Review of the balance of competences between the United Kingdom and the European Union - Civil Judicial Cooperation.
: Since the UK is a dualist State, any treaty that it ratifies does not give rise to new laws until it has been integrated into domestic law by a national law. Regarding the European Convention on Human Rights, the text integrating these measures into national law is the 'Human Rights Act of 1998 that entered into force in 2000 which provides that the UK's law be in line with those of the ECHR.
: At the end of 2013, there were 2,517 cases pending at the European Court of Human Rights involving the UK, 2000 of which were cases that had already been previously processed, most regarding prisoners' voting rights.. Cf. Review of the balance of competences between the United Kingdom and the European Union - Fundamental Rights.