Mr Cameron, increasingly seen as the favourite to win, took a swipe at Mr Davis's responsibility as home affairs spokesman when he ventured on to his rival's specialist subject. "The police are the last great unreformed public service. Politicians shouldn't treat them with kid gloves just because police officers do such a brave job in protecting us,'' he said.
The "Two Davids" are due to go head-to-head on the BBC's Question Time tomorrow, and Mr Cameron's remarks suggest their debate may live up to its billing as a showdown. They will stand at lecterns for the duration of the presidential-style debate.