As a sort of knee jerk reaction, it seems to make sense in denying these people reentry to the UK, in effect making them stateless.
But if you think about it a little harder - what happens if you have several hundred or thousands battle-hardened, brainwashed, chav terrorists and you "send them back" isn't that sticking your head in the sand? Effectively, you're putting them back into circulation in the world - where they might cause additional harm, they could fade away in some other hellhole - only to come back later and bite us in the ass.
Wouldn't it be safer to imprison them upon entry? If we have the intelligence to know that they're terrorists - why risk "throwing them back out" why not just use all available methods to track them, and detain them if they come back.