Boris Johhnson has said he will stump up the cash to rezone Kingston and Surbiton station in answers given at the Mayor of London's Question of Time.

But he has told Liberal Democrat members of the London Assembly he has no formal powers in moving the stations from zone 6 to zone 5 which could save commuters hundreds of pounds a year in fares.

Both stations are only 12 miles from London, much closer to the average distance for zone 5 stations.

Mr Johnson said: "I have now written both to Ed Davey and the Secretary of State expressing my support for this campaign and I shall be happy to raise the issue at my forthcoming summit with the train companies.

"However, as Mayor, I have no formal powers in this area.

“This initiative will therefore only come about as a result of pressure put on South West Trains (SWT) by the local people affected.

"Given the way the National Rail train franchising system operates, it is SWT that must formally propose any change to the way these stations are zoned and then seek the agreement of the other London train companies, and the consent of the Secretary of State for Transport and of TfL.

"There would be some loss of revenue to the Tube and buses if travel cards from Surbiton and Kingston were rezoned.

"However, in the event of a rezoning proposal coming forward from SWT for my approval, I shall be happy to give it my consent without seeking any compensation from either SWT or the Secretary of State."

In July, Kingston and Surbiton MP Edward Davey attacked Mr Johnson for "broken promises" after he failed to arrange a meeting to discuss the rezoning.