Cameron's next European 'faux-pas'

Britain is now mulling an important decision which, despite being fiddly and legalistic, has profound implications for its own security and for Europe. Should its government withdraw from EU co-operation on cross-border policing and justice, as the UK has the right to do under a special deal negotiated under the Lisbon treaty? MPs are likely to say 'yay' when Britain's parliament votes on the matter next year: anti-EU feeling is at an all-time high in Westminster.

The ins-and-outs of this are unusually complex. Britain fears the impact of new powers given to the European Court of Justice (ECJ) over criminal justice and policing. Under the EU's Lisbon treaty, the court will gain full jurisdiction over all justice and home affairs (JHA) matters from 2014 onwards. This includes around 130 JHA ‘decisions’ in place before Lisbon came into force in 2009. These agreements are more loose international accords than proper legislation. But, after 2014, they will become as binding on EU countries as single market regulation, meaning that, for the first time, the Commission can enforce them and EU judges can interpret their exact meaning.

If Britain does exercise this 'mass opt-out', almost the entire JHA acquis will cease to apply to it. That means the country will no longer have to fear how EU judges might interpret fairly insipid measures such as minimum EU rules for punishing rascism and xenophobia. But it will also lose key tools like the European arrest warrant, the jewel in the crown of JHA co-operation. Europol, the EU's police office, and Eurojust, its unit of national prosecutors, will no longer be able to handle British requests for assistance. And the UK will not be able to use a range of databases and cross-border agreements designed to help EU countries maintain security and manage the free flow of people between them. (A common EU criminal records database and arrangements for transferring prisoners between member-states are two examples).

Britain is often a curmudgeonly negotiator. But it is normally quite good about implementing EU deals once they are concluded, whether the Commission acts as policeman or no. So, what is its problem? The criminal law of most EU countries is based on a mix of the Roman civil law and the Napoleonic legal code. Of the large member-states, only Britain uses common law, a fundamentally different legal system, where the defence and prosecution battle out cases before a neutral judge and jury. Other EU members have always recognised that Britain (and Ireland, another common law country) are unique in this respect. That is why both countries are allowed to opt in to EU laws on justice, migration and internal security on a case-by-case basis.

Under the Lisbon treaty,  the EU has shifted the emphasis of JHA policy from 'co-operation' to a limited form of 'integration'. The UK government fears judicial activism on criminal law from the ECJ, of the same type that EU judges have previously displayed in single market legislation. (British Conservatives probably fear and dislike the ECJ more than other EU institution.)  Over time – the thinking in Whitehall goes – the ECJ could undermine the common law and its ancient traditions in favour of the continental legal model that the great majority of its judges know best. Hence the Lisbon treaty's special arrangements for Britain and the temptation for its government to get out before the option to do so is lost after 2014.

But this would be a costly mistake for Britain for several reasons. First, the British establishment believes that having triggered the mass opt-out, its size and importance mean that it will be able to opt back in to some measures – say 40 or so, including the arrest warrant – that it does find useful. That is an arrogant assumption. The European Commission is likely to attach tough conditions to allow Britain to do this. (Denmark opted out of this entire policy area after rejecting the Maastricht treaty in 1992 and has only been allowed into a handful of specific JHA measures ever since.) Recent history also suggests that other EU countries would object in principle to British cherry-picking. Schengen area countries have blocked British access to Frontex, the EU's border agency, and the so-called VIS, a database of Schengen visa records, because of the UK's decision to maintain its own, separate border controls. Why should they assist Britain in following an a la carte agenda in policing and justice, too?

Second, Britain has shaped much JHA policy to date, especially in counter-terrorism. This is a remarkable diplomatic success for a country that is not in Schengen, possesses a minority legal system and selectively opts-out of common rules. Partly, the reason for this is that Britain has very clear ideas about how best co-operation between police, judges, border guards, customs officers, immigration officials and other public authorities should be organised to mitigate the negative aspects of free movement. It is no co-incidence that the current head of Europol, Rob Wainwright, is British, as have been the last two presidents of Eurojust, and the last two director-generals of the Commission's JHA directorate.

This precious influence would be thrown away should Britain go down the mass opt-out route, which would be seen as a bridge too far. Most of Britain's EU partners have not yet guessed how much of a done deal the mass opt-out from JHA policy already is in the Westminster village. For British eurosceptics, the opt-out is “low hanging fruit” in their attempt to push the UK  towards an EU exit. Even traditional allies like the Netherlands and Sweden are likely to take the surprise badly: the move could be as bad a diplomatic faux paus as David Cameron's veto at the EU summit in December 2009.

Why does all this matter? If Britain's JHA wheeze backfires, its government will still have to apply EU free movement rules. These are part of the single market. But the UK's Home Office, border services, police officers and intelligence agencies could be locked out of the tools that mitigate the impact of these rules on domestic security and public order. If it cannot re-enter the European arrest warrant, for example, Britain risks becoming like Brazil, a place where Europe's criminals go in the knowledge they will be safe from extradition. British ministers in the Home Office – that graveyard of political careers – may face enquiries about why they cannot secure better support from their EU counterparts in the teeth of future crises. Arguments about the sanctity of the common law are likely to ring hollow then.