By politics.co.uk staff
Jon Cruddas, a crucial figurehead for the Labour left, has backed Ken Livingstone in his bid to become London mayor for a second time.
The support will give Mr Livingstone's campaign a major boost as he battles it out with former Bethnal Green and Bow MP Oona King to become the party's official candidate in the mayoral election.
Mr Cruddas' union and activist connections mean he brings a substantial voting block to Mr Livingstone's side.
"London has faced economic upheaval in recent years, and will soon come under serious attack from the national government as it imposes a series of devastating cuts on the services Londoners rely on," Mr Cruddas is expected to say later today.
"The mayor of London can play a big role in defending Londoners from these cuts and building an alternative to the Conservative agenda.
"Labour needs a candidate who can win in 2012, uniting the party and taking the fight to a Boris Johnson administration that has let Londoners down. Labour needs a candidate who will be a first-rate mayor from day one, who knows the levers of power, and how to use power in the interests of all Londoners.
"For me, Labour's candidate must be Ken Livingstone. He has my vote, and I call on all Labour members to unite behind him, too."
London mayor Boris Johnson faces the mayoral election in 2012.