I knew a member of the Met armed unit when I lived in Epsom and he once said if he is facing a gun man it is a case of him or me so instructions to shoot to stop him go out of the window. He would do that if the person was running away but not if facing him with a gun.
I would have thought that if they shot a man just to stop or down them but not to kill could they not operate a hand held detonator be it a suicidal bomb or not.