Ken Livingstone weighed into the Labour leadership contest today by hailing Ed Balls as a "fighter" who had done most to boost London.
In a letter sent to all Labour Party members, he said he had worked with all the candidates as Mayor and found Mr Balls the most effective.
Crediting the former schools secretary with sourcing the funding for Crossrail and implementing the London living wage in his department, Mr Livingstone urged: "Ed doesn't just talk the talk but gets things done."
Mr Livingstone also backed Diane Abbott and Ed Miliband in the contest, where voters can rank candidates in order of preference.
In a speech tonight, shadow foreign secretary David Miliband will say Labour must attract the middle classes in the South as well as core supporters in the North — an apparent attack on his brother Ed.
He will say some candidates wrongly wanted to retreat into a "comfort zone" and Labour lost the trust of voters before the election.
"The fact that they are wrong matters less than the fact that we are not trusted. We are pigeonholed as profligate when we need to be frugal; we are seen as statist when in fact our mission is to empower individuals, communities and businesses; and we are seen as the Establishment when we need to be the radicals."
His speech has been billed by aides as the most important of his campaign, coinciding with him nothing up his 100th MP supporter.
"There is no future for Labour in the comfortable but deadening policies of the past," he will say.
"And there is no future in a politics based on a tactical, patchwork approach to building electoral support."
