Labour's Mayoral candidate Sadiq Khan has been called on to explain the true level of his contribution to London's first Crossrail project.

On a number of occasions in his mayoral campaign, Mr Khan has stated he 'led' on the multibillion pound railway project.

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One campaign leaflet features a picture of Mr Khan in high-vis, safety glasses and a hat in a tunnel with a caption that reads: "This gave me the experience to deliver. I led on big projects such as Crossrail."

In an interview with the Wandsworth Guardian, he said: "Crossrail 2 is hugely important, I was the minister in charge of Crossrail 1, which goes from east to west London and regenerated London."

City Hall commentary website Mayor Watch first picked up the unreliability of Mr Khan's claims in July.

His role as Minister for Transport only began after building work on the project had started.

The Crossrail Hybrid Bill was presented to Parliament in February 2005, three months before Mr Khan won his seat in Tooting.

The Bill received Royal Assent in July 2008, when Mr Khan was a backbencher, four months before his appointment as Minister of State for Communities.

The Crossrail Act 2008 in July, gave the confirmed route.

In May 2009, Crossrail broke ground in Canary Wharf.

Mr Khan was appointed Minister of State for Transport in June 2009 until May 2010 when Labour were ousted from Government.

A spokesman for Mr Khan said: "As minister, he had responsibility for the line and for taking the Bill which funded it through the Commons.

"He is not claiming credit for getting it started.

"Sadiq was in charge of the Business Rates Supplement Bill when a Communities and Local Government Minister which was the Act that paved the way for the Business Rates Supplement which contributes £4bn to Crossrail.

"Sadiq was also the Minister with responsibility for Crossrail 2009-2010, which includes delivery of the building of the line during that period."

According to the Crossrail website, the funding framework was agreed in October 2007, and £14.8bn was agreed for the scheme following the Comprehensive Spending Review in October 2010 - by which time Mr Khan was back in the opposition.

A November 2007 document, called Heads of Term for the Crossrail Project, gives confirmation that funding will be provided from Government, even if the supplementary business rates provision is not in place.

The document states: "If the new legislation is not in place to enable the GLA (Greater London Authority) to receive revenues from supplementary business rate commencing no later than April 1, 2010, or the legislation provides insufficient powers, then provided DfT (Department for Transport) is satisfied that appropriate funding from this course will still be forthcoming, DfT will provide an additional grant to the GLA equal to the equivalent amounts that would have been received form such a supplement and will provide temporary guarantees in respect of any additional debt rained by the GLA during the interim period attributable to the delay."