Since the demise of PIRA, OIRA, RIRA and any other IRA groupings, we've been lucky enough to have been pretty much terrorist free for a good few years. At one time 'Christmas London Bombing Campaigns' were the norm.
Being ex-forces, as many other members are here, I remember the low-level counter-terrorism tactics that were used by the British Government, such as adverts saying, 'If you see unatended bags - report it'.
But now we've an 'X' factor; religous extremism - maybe even suicide bombers. I don't think it's got much to do with imigration. Just nutters. The USA is heading towards the 'religious nut' direction also.
We've plenty of our own 'home grown' terrorists. The thing is, sadly, law-abiding people from ethnic backgrounds will now suffer also.
Luckily, I've got slanty-eyes, so I won't be targeted as a 'Muslim Terrorist', but you just know many dark-skinned people will; even though they are as British as you and my dog.
There is no easy answer.