PMQs: Cameron on Livingstone, Johnson, buses and taxes
21 March 2012 Last updated at 13:25 GMT
David Cameron hit out at Labour's London mayoral candidate Ken Livingstone over allegations over his tax affairs.
He was asked by Labour MP Huw Irranca Davies about the cost of bus journeys in London, but the prime minister hit back saying that Ken Livingstone did not keep to previous pledges to freeze fares.
David Cameron said: "The difference between Boris and Ken is that Boris pays his taxes - and Ken doesn't."
Mr Livingstone had previously denied claims he has not paid tax on his income, saying he was the victim of a "smear campaign".