A fictional "scenario" of multiple bomb attacks on London's underground took place at exactly the same time as the real bomb attack on July 7, 2005. There have been several documented cases of mock terror drills in the US and the UK, held prior or on the same day as the actual terror event.
There is no special police licence to injure or kill. If they injure or kill, the police need to rely on the same law as the rest of us. It is no defence in law that the killing was authorised by a superior officer. A superior officer who authorises an unlawful killing is an accomplice.