AB's finest legal mind (apologies to Barmaid and New Judge) has given the reasons why returning jihadis cannot, or perhaps should not be prosecuted. Summed up (rather well, I thought) by Ichkeria's "scrabbling around raking up old laws and trying them for size because nothing else fits is probably doomed to failure".
Perhaps, then, Peter Pedant will suggest what new legislation might be effective in protecting the Queen's Peace.
I'm assuming, of course, that PP accepts that the Queen's Peace is threatened by returning jihadis, the 25,000 "extremists" known to the security services and sharia-promoting Deobandi clerics, some "refugees" and so on. Maybe he doesn't.
I'm assuming, too, that the maintenance of he Queen's Peace is still a concern of the Law. But maybe that concern has been subordinated to - or even replaced by - other concerns like maintaining social cohesion. Who knows, eh?