Frankly, if you believe that people running the MI5 or the CIA would be willing and capable of doing something like that, I think you have a very distorted view of reality in this regard. Unfortunately, the inferential distances are probably too large for us to have a productive discussion about it in this context.

The CIA assassinated a US citizen not two months ago, and the government made no attempt to hide it out of an (accurate) expectation that the public would approve. Of course I doubt the FBI has killed a white person on US soil by blowing up their apartment recently, or will in the forseeable future, but if we allow probable facts about national character to be this specific it seems that trivially any fact about what a government is likely to do is a fact about its national character.