Colourful London mayor Boris Johnson played down talk of him challenging David Cameron on Tuesday, describing the prime minister as a broom who was sweeping away the British economy’s problems. Johnson said Cameron would win re-election in 2015 and even wished him a happy birthday from the podium at the Conservative Party’s annual conference, where the mayor has been treated like a rock star since his arrival. Pointing to Cameron in the audience in Birmingham, Johnson said in his keynote conference speech: “I know that David Cameron will win in 2015, when the economy has turned round. “We are already seeing signs of progress, when people are benefiting from jobs and growth and the firm leadership you have shown and the tough decisions you have taken – not least coming along to hear this speech today.” Speculation has been rife that Johnson wants the job of his former school and university contemporary, and opinion polls have shown that he has a far higher popularity rating than Cameron. But in typically eccentric style, Johnson, who is known for his distinctively dishevelled blond hair, paid tribute to the prime minister as he celebrated his 46th birthday. “I was pleased to see that you called me a blond-haired mop in the papers. If I am a mop, David Cameron, you are a broom – a broom that is clearing up the mess left by the Labour government, and a fantastic job you are doing,” he said. To laughs from the audience, Johnson went on to describe finance minister George Osborne as a “dustpan” and foreign minister William Hague as a “sponge”. Johnson also told an anecdote about how he and the prime minister had danced to the South Korean pop hit “Gangnam Style” together recently as proof of their close relationship, although he did not provide details. The London mayor did, however, take the chance to set out his own vision for boosting the economy, saying that Britain should capture the “can do” feeling it showed during the successful staging of the London Olympics and Paralympics.