A perk that grants free travel to the flatmates of TfL staff now costs London taxpayers more than £33m a year in lost revenue, according to new figures.

New research undertaken by the London Assembly Conservatives claims that staff handing out free travelcards to friends, lodgers, family members or anyone else living at their address comes at a cost of £33.3m a year.

The perk is said to be not part of the employee contract and could be rescinded by transport bosses at any time.

Redbridge’s London Assembly member Keith Prince wants the Mayor to scrap the “ridiculous and unnecessary” bonus and instead offer firefighters free travel at a fraction of the cost.

He said: “It seems ludicrous that the taxpayer has to foot a bill of over £33million a year just so TfL staff can hand out free travelcards to their mates.

“It would be hard enough to justify this perk under normal circumstances, but at a time when the Mayor is seeking to save more than £640million from within TfL because of his disastrous fares freeze it really takes the biscuit.

“The Mayor needs to scrap this ridiculous and unnecessary perk immediately. By doing so he could save TfL and the taxpayer millions in vital revenue and still have money left over to provide our firefighters with a valuable thank you for their work.”

City Hall has contested the figures claiming they are simply incorrect.

A spokesman for the Mayor of London said TfL would only gain additional revenues of just £5m a year if all passes were withdrawn - based on journeys that would actually be taken and paid for.

He said: “Keith Prince’s figures simply aren’t correct. He should act more responsibly, rather than making misleading promises to Londoners that aren’t deliverable.”

Sadiq Khan has also already asked for a review of free travel for nominees of staff earning more than 100,000 pounds a year.