Each side in the EU referendum debate is determined to put the best possible slant on its case and the worst possible one on its opponents’.  This is invariably so in other matters too, but is especially the case here, given what is at stake.  So it is that many Remain campaigners strain to persuade voters that a British vote to leave the EU will unleash a takeover by triffids (which is more or less the sum of Jeremy Hunt’s risible intervention today about the NHS), while their Leave equivalents strive to convince them that the same result will usher in the age of Aquarius.

ConservativeHome is for Leave, on the ground that Brexit will bring five main gains – fewer politicians, better immigration control, more money for public services and tax cuts, a stronger economy and global engagement – and that the risks of Remain are greater than the risks of Leave.  But beware of anyone who claims that all arguments in every aspect of discussion come down unambiguously on one side of it.  He is almost certainly putting his conclusion first and his case afterwards, like a man walking backwards before royalty.

So it is with security – a red-hot topic in the aftermath of the Brussels atrocity last week, the two recent terror attacks in Paris, and the fear, raw and real, of more 7/7s in Britain. The debate continues in today’s papers.  I think the balance of consideration on security, as well as more broadly, is for Leave, but the operative word really is think: one has to try to ponder one’s way through a thicket of points made either way, few of which have no merit at all.  They essentially break down into four categories: co-operation, intelligence sharing, border control, and the courts.

By co-operation, I mean mechanisms such as Prum, the European Criminal Records Information System, the European Arrest Warrant (EAW), and so forth.  There is a civil liberties case against all these developments – consider the case of Andrew Symeou and the EAW –  but the thrust of the security one is for them.  It might well be possible to keep their benefits while outside the EU (for example, by negotiating a special extradition treaty with it rather than cleaving to the EAW), but there must be a questionmark over whether such an outcome could be achieved swiftly.

Furthermore, it can be argued that it is Britain’s membership of the EU which is leading it to up its security game.  Consider the case of the Passenger Name Records Directive, which would give the authorities access to airline passenger data for people travelling on international flights.  The European Parliament blocked the proposal in 2013.  It is expected to pass through it soon.  Without British pressure, there might be no records of, say, Greek flights to Belgium for security services to thumb through.

But if the balance of the co-operation case falls on the side of Remain, that of intelligence sharing leans clearly towards Leave, or at least to neutrality.  By intelligence sharing, I mean the sharing of security information outside EU mechanisms.  From Britain’s point of view, our most important partners is this process are not EU countries at all – but, rather, those of the “Five Eyes”, especially the United States.  None the less, intelligence sharing with some EU member states, especially France, is obviously important.

However, Britain’s interest in sharing information with France, and vice-versa, has nothing to do with Britain’s EU membership.  To put it simply and plainly, both are western democracies under a common threat from Islamist extremism.  The risk to one is also a risk to the other.  It follows that France would be cutting off its nose to spite its security were it to compromise intelligence sharing in the event of Britain leaving the EU.  The same applies to other EU member countries.

This brings us to border control.  A key argument of some Remain supporters is that free movement must not be confused with Schengen – and that since we aren’t in the latter we are able to control our borders.  It is worth pausing on the point about Schengen.  It doesn’t follow that it poses no problems for us simply because we aren’t in it.  The recent Paris attacks were a grisly reminder that a suspect can move from a part of Europe relatively close to Syria, such as Greece, to one separated from Britain only by a strip of water, such as France.

Furthermore, that there are checks on free movement is no guarantee that these deliver the security goods.  Mohammed Abrini, the “man in white” of the Brussels atrocity, reportedly visited Britain last summer.   The systematic checks on EU citizens are more narrowly drawn than those carried out on non-EU ones.  “The long and the short of it is that it’s easier to keep out, say, Zakir Naik than, for example, Geert Wilders,” one source told ConservativeHome, referring to the bans served on the Indian preacher and the Dutch politician.

This is a reminder that border control and legal decisions turn out to be inextricably intertwined.  And while the role of the European Court of Human Rights (ECHR) is widely known, that of the European Court of Justice (ECJ) is less so.  The ECJ has the final say on the Charter of Fundamental Rights – yes, the same Charter of Fundamental Rights that Tony Blair assured the Commons that Britain had an opt-out from.  This gives it the authority to determine what powers our own intelligence agencies and police have to protect us.

It also interprets the 1951 UN Convention on the Status of Refugees.  Our columnist Nick Timothy, who served as a Home Office SpAd during the Coalition, has written on this site that the ECJ “can be expected to become even more aggressive in its human rights rulings than even the European Court of Human Rights”.  For example, it recently published a preliminary opinion that the daughter-in-law of the terrorist Abu Hamza could not be deported from Britain: she has a criminal conviction and is not even an EU citizen.

It is hard to argue convincingly that British judges interpreting a British Bill of Rights would not show a greater sensitivity to our Parliamentary culture than the ECJ’s – or indeed than the ECHR’s.  There is learned dispute about whether it is or isn’t necessary first to leave the EU in order to leave the ECHR.  What is certain is that quitting the first would make it no harder to depart the second.  And the ECHR has certainly proved an obstacle when it comes to putting security at the forefront – as in the case, for example, of Abu Hamza himself.

There are counter-arguments.  For example, Leave can say that the “third party rule” of international intelliegence sharing, which states that information passed by a first to second country cannot be passed from that second to a third without the first country’s consent, makes real intelligence sharing between EU states impossible (at least, if secrecy is to be preserved).  However, Remain will say that Britain would not escape from free movement by leaving the EU, any more than Norway or even Switzerland have, unless it wants the doors to the single market closed.

The prospect of escaping the jurisdiction of the ECJ – and perhaps in time the ECHR – should in my view be decisive.  But this debate requires a salutory footnote.  The biggest threat to our national security runs much deeper than controversy about Britain’s EU membership.  Three British men, originating from the Indian subcontinent, carried out 7/7.  The fourth was a convert to Islamist extremism born in Jamaica.  Neither leaving the EU nor remaining in it will dampen the fanaticism of the home-grown extremists bent on carving pre-modern ghettoes from British democracy.