Sadiq Khan
Sadiq Khan, a former Labour frontbencher, promised to roll up his sleeves and 'fight for all Londoners'Getty

Sadiq Khan has launched his campaign to become the next mayor of London but he must first beat a strong line-up of Labour colleagues to become the party's candidate.

The Tooting MP was tipped to run for the role and he has now made the move official while attacking Tory incumbent Boris Johnson.

Khan labelled Johnson, elected in 2012 for the second time, a celebrity mayor and promised to "fight for all Londoners".

"For the last eight years you've seen a red carpet mayor, somebody who is fantastic going to openings, great with a flute of champagne in his hands. I'd rather roll up my sleeves and fight for all Londoners," he told the Evening Standard.

Khan, 44, comes from working-class stock – his father was a bus driver – and he became the second-ever British Pakistani to serve in the UK government as communities minister under Gordon Brown.

He left Labour's shadow cabinet just days ago, where he served as the party's spokesman on justice and London.

The move came after Labour lost the general election and saw David Cameron and the Tories sail into Number 10 with a slim majority of MPs in the House of Commons.

Ed Miliband quit soon after the devastating result triggering a leadership contest, with deputy Harriet Harman announcing she would become interim leader before standing down from her original role once a new leader was chosen.

Khan faces stiff competition in the shape of David Lammy, Tessa Jowell and Diane Abbott to become Labour's mayoral candidate. Lammy, the MP for Tottenham, had a head-start over the other runners after he declared first in September 2014.