forget internment, take the 500 cases, revoke their UK citizenship or immigrant rights as they clearly don't want to be here and deport them to Syria/Libya/Pakistan wherever...inc Saudi.
I would personally leave the back door of the 707 open but that wouldn't be politically acceptable - but then Spooks did it.
However, back to basics, it would send a hell of a message about our country's want and intent to act against such despotic acts - not a bastion of Christianity but a bastion of decency for all religions, even including the sensible and God-fearing Muslim.