He was London educated and had been living here. What if he had decided to set something off here would that bring it back home for you!?
He was also reported to authorities by his father, and this information was not acted upon. Still, this does nothing to change the fact that the attack was not on UK soil, or a UK flight and so UK anti terrorism legislation would have had no jurisdiction.
I'm sure we have had people who were or still are members of the IRA living here or educated here as well. I am unsure of the point you are failing to make? Unless you propose to ban anyone living here who has a funny accent, a bit of a beard and dark skin? In which case, I'm ****ed.