David Cameron has sparked a furious row over the contest for the London mayoralty after he accused Labour candidate Sadiq Khan of sharing a platform with an Islamic "extremist".

Angry Labour MPs accused Mr Cameron of racism during Prime Minister's Questions in the House of Commons as he detailed Mr Khan's nine appearances alongside Sulaiman Ghani, who he said was a supporter of the Islamic State terror group.

A senior Labour source later accused the Prime Minister of "demeaning his office", while Mr Khan himself said he was "disappointed" Mr Cameron had chosen to join a "dog whistling" campaign by London Tories.

Mr Khan, who is bookmakers' favourite to replace Boris Johnson at City Hall in the May 5 election, has faced repeated claims that he has given the oxygen of publicity to extremist individuals by appearing alongside them, though Conservative candidate Zac Goldsmith stressed he does not accuse his rival personally of extremism.