Ron Davies, the British police had already been trained in Israel. That's one of the places where they learned about having to completely disable a potential suicide bomber.

Reuters

"'I sent teams to Israel and other countries hit by suicide bombers where we learned a terrible truth,' he wrote in the News of the World.

'There is only one sure way to stop a suicide bomber determined to fulfil his mission -- destroy his brain instantly, utterly. That means shooting him with devastating power in the head, killing him immediately.'"