Former MP Oona King is expected to announce this week that she will challenge Ken Livingstone to become Labour’s candidate for Mayor of London.

If selected she would be taking on current Conservative Mayor, Boris Johnson, at the election in May 2012.

The contest will take place during Labour’s conference in September, the same week the Miliband brothers will be battling it out for the party leadership.

King, who has a Jewish mother, lost her Bethnal Green and Bow seat in the 2005 general election to Respect’s George Galloway by just 823 votes.

She was first elected as an MP in 1997 and now works as head of diversity at Channel 4.

Last month she told a newspaper she was ‘very interested’ in the role.