If British Muslims want to leave it to fight in Syria and Iraq, where they may learn terror tactics to use here on return, they should have their passports removed.  And if they get to those countries and then try to re-enter Britain, they should be barred from doing so – at least, until or unless they’re willing to face prosecution.

Such will be the straightforward view of many voters, though there are at least two groups of dissenting voices.  The first are the cynics who are happy to see would-be jihadis travelling to a war in which they may be killed.  (But they may not be, and may thus find ways of re-entering Britain, trained in terror, to cause mayhem and slaughter.)  The second are the purists who believe that citizens of any country have an automatic right to immediate return, even if they add that any who are terror suspects should be charged and put on trial.

David Cameron’s announcement in Australia on passport removals and entry restrictions comes at a time when about 500 British Muslims are said to be fighting in the Levant, 30 to have been killed there, and 250 to have returned – although these estimates are rough and the real figures may well be higher.  The two main elements of his policy are as follows. First, he proposes to widen the grounds under which passports can be removed from terror suspects (only 24 have been to date) through a new offence of “reasonable suspicion” that they are planning to join a terror organisation.  Second, he wants bar suspects from re-entry for at least two years, though they will eventually be able to enter to face prosecution, restrictions on movements or de-radicalisation programmes.

Those who volunteer to be prosecuted or monitored may be admitted earlier – and it is this possibility that allows the Prime Minister to claim that government would not be rendering such people stateless.  We may see what the courts make of that.  It could be that he would have liked the time-frame for the ban to be longer, and has chosen one that he thinks will stand up to legal challenge.  Quilliam argues that jihadis should be encouraged to return home and face prosecution rather than be forced “to stay in a crisis zone and further radicalise either themselves or others in the UK through their online activities”.

Perhaps – but some will not wish to surrender themselves to the authorities and may plan to carry out terror attacks in Britain.  One can see why Cameron is trying to stretch the law on statelessness as far as it will go.  Quilliam is also dubious about the proposal to remove passports, saying that the ground of reasonable suspicion must be “intelligence-led…[and] not become a policy reminiscent of stop and search, which resulted in cases of racial profiling”.  It would certainly be an irony were Theresa May, who is reforming stop and search at the front door, were to see it reintroduced as a counter-terror measure at the back.  But the Government cannot duck the security challenge thrown down by the would-be jihadis.

The idea of travelling from Britain to the Middle East to cause carnage is not only being spread by the YouTube posts and Twitter proclamations that the Prime Minister wants the owner companies to crack down, but through friends and contacts – as Shiraz Maher and others have pointed out.  The scale of the problem is unknown, but the risks are great.  We have been spared a mass attack on civilians since the Glasgow Airport attack in 2008, thanks in no small part to the security services. Although they have missed some terror plots, they have almost certainly prevented more.

Now Cameron must win the battle within Government over the return of powers to relocate suspects away from their home areas.  These were a feature of Labour’s Control Orders (themselves flawed) which went out with TPIMs because of Liberal Democrat pressure – or so the Home Office says.  This is a struggle the Prime Minister must win.