They all should be stripped of their UK citizenships and sent back to their countries of origin.
This would have been some of the most effective measures, but I have never seen any Western nation doing it. The citizenship must be revoked not only for the attacker, but also for his family members. This can be even more effective than sentencing the terrorists to death.
What is this, fucking 1984, are you guys actually serious? How about we treat every criminal the same, that's the way justice is served in civilised countries. You are no better than the terrorists with your chants to "send their families back!!". Oh, and good luck revoking the citizenship of some scattered body parts...
Not to mention the majority of terrorist attacks in the UK are not by recent immigrants but by 2nd or 3rd generation immigrants. And that there are orders of magnitude more people killed in places like Iraq and Afghanistan, than the UK.
You are just helping the terrorists with your scaremongering - stand up tall and say "bomb us again motherfuckers, we will not stoop to your level!"
That is how you beat terrorism like this, not by cowering in the corner and "stripping the terrorists' relatives of their UK citizenship"
like that's gonna change anything...