Cats have nine lives, and if they were measured in terms of prime ministers, spare a thought for Larry. He must be wondering whether he will soon be on his seventh. That makes the Downing Street moggie a pensioner. How he must wish he had a triple lock on the No10 door to prevent another PM from escaping. Larry was brought in by David Cameron from Battersea Dogs & Cats Home in 2011 and given the official title of Chief Mouser to the Cabinet Offi…