Boris Johnson last night said he could "absolutely guarantee" that Tramlink would be extended to Crystal Palace by 2020.

Speaking at a Conservative Party fundraiser, the Mayor of London said the much sought-after extension has been approved by Transport for London commissioner Peter Hendy.

But he added a precise timeframe for the extension was yet to be established.

Mr Johnson said: "It is a very slow-moving process but it is going to happen. 

"It may not be by 2015 but it is going to be by the end of the decade. I can absolutely guarantee that."

Mr Johnson and TfL has come under repeated fire in the past for failing to allocate funds for the extension despite publicly backing it.