Sadiq Khan attempted to secure a generous "repayment holiday" on a government bail-out of Crossrail in order to avoid breaking a manifesto pledge to freeze tube fares, Government sources have claimed.

The Mayor of London approached the Department for Transport last year to seek a loan on which Transport for London (TfL), which he chairs, would have been spared capital and interest payments for several years.

A Government source claimed that the terms he delay he requested for repaying the loan was "outrageous" because it would have "postpone[d] the consequences of failure to the next mayoralty", meaning Mr Khan could avoid putting up tube fares in the capital before the next mayoral election in 2020.

Ministers were told that the request for a "repayment holiday" was intended to ensure that repayments would only begin once the line had opened and TfL was receiving revenue from ticket sales.

But the Government source said: "He essentially asked for a very long loan with an interest free period to begin with, which of course would have had the effect of postponing any difficult decisions until after his mayoralty. It would be future generations of Londoners who would have to pick up the bill and he wouldn't have to make any serious choices, particularly around whether to raise fares or not. Even assuming that he was re-elected it would postpone [the decisions] for several years."