Clapham Junction will be connected to the Northern line, according to London Assembly member Richard Tracey.

The UK’s busiest station is not connected to London Underground, but with the planned extension of the Northerrn line to Battersea, discussions are under way to create a huge transport hub at Clapham Junction.

A path running beneath Battersea Park has already been reserved for such a move and Mr Tracey, who represents Merton and Wandsworth, believes it is a matter of “when not if”.

He said: “We have always seen it as a far distant possibility, although now with the proposed Northern line spur to Battersea Power Station and Nine Elms getting nearer to reality it makes our dreams more feasible.

“An underground route to Clapham Junction roughly under Battersea Park is apparently safeguarded so that avoids many potential planning problems.

“I think the point that also strengthens the case is that Clapham Junction is rapidly becoming an even more important transport hub with the existing mainline services and with the new Overground, which is so popular.”

Clapham Junction would only be connected to the Northern line once the current construction of a spur at Kennington and two new stops, at Nine Elms and Battersea Power Station, is finally completed.

Work on that extension, in tandem with the multi-billion pound Nine Elms development, is set to begin in January 2015 with a view to completion by approximately 2020.

Richard De Cani, Transport for London’s (TfL) director of transport strategy, said this work would be designed to allow for further extension.

He said: “Clapham Junction is hugely significant as a destination and interchange point.

“The plans for the Northern line allow for an extension of the lines to Battersea to go Clapham Junction.

“That’s why we’ve planned the Northern line extension as we have, so it can be included in the future and that’s why it is included in the options for the Crossrail 2 consultation.”

Wandsworth Council leader Ravi Govindia said the local authority had been pushing for a link and would continue to do.

He said: “We are pursuing two very good prospects for connecting Clapham Junction to the Underground network.

“The first is a ‘phase two Northern line extension’, which would see the new tunnel extended further to reach the Battersea interchange. “We are also pressing for the proposed Crossrail 2 tunnel to include a stop at Clapham Junction and have asked TfL to consider how this new underground line would connect with the Northern line extension.”

Annoucing his new transport policy for Londo, called 2020Vision, London Mayor Boris Johnson said he wanted to see all available rail capacity taken up, on existing and new tracks.

However, there is a limited pot of cash for future development in the capital so a potential extension to Clapham Junction would have to see off competition from other projects in London.