Johnson 'can do anything', including be PM, says Cameron An admirer: British Prime Minister David Cameron says Boris Johnson can do almost anything. British Prime Minister David Cameron has admitted that one of his biggest party rivals, London mayor Boris Johnson, could well be a future prime minister. Mr Johnson is considered a potential challenger for Mr Cameron's leadership of the centre-right Conservatives. However, Mr Johnson's second mayoral term runs into 2016 - and the next general election must be held by May 2015. Asked if Mr Johnson could combine being London mayor with a return to Parliament, Mr Cameron said: "Boris can do anything, that's the moral of the story of Boris." Mr Cameron insisted he did not feel threatened by Johnson's ambition or popularity. Boris is one of the greatest assets the Conservative Party has. I love Boris," he said. Asked whether Mr Johnson could become prime minister, he said: "I'd never want to put a limit on what Boris can achieve." Mr Cameron and Mr Johnson were in the same exclusive dining and boozing society at Oxford University, the Bullingdon Club. Mr Cameron caused a stir on Thursday by appointing Mr Johnson's brother, Jo, his head of policy.