A new park 20 times larger than Hyde Park, 10 times the size of New York's Central Park - and technically big enough to be seen from space - could be coming to the borough.

The 13sq m site, dubbed a "regional park for London", will straddle Merton, Wandsworth, Sutton and Croydon, stretching along the River Wandle to the Thames.

As part of Mayor Ken Livingstone's London Plan, green charity Groundwork is launching a consultation on the project that will connect all the green spaces in the Wandle valley.

Improved transport links to the area and a state-of-the-art visitors' centre are among the other ideas that will be presented in a formal vision for the project this June.

Angela Gorman, Groundwork development manager, said: "It is vital everyone gets to have their say about this fantastic opportunity for London.

"Not only will it be a place to relax, exercise and enjoy being outdoors, it is also central to the regeneration and future prosperity of this area and the vital connections between the built up areas and the riverside.

"The Wandle valley is a really under-used hidden gem of south London. People won't believe they have lived near a place like this for so long which they're yet to discover."

John Bishop from the Wandle trust said there was "no question" the park would be a great thing for the Wandle. "Within the next 10 years I'd like to see all the industrial sites removed and the river restored. We should even be thinking about removing housing where possible," he said.

But south London nature expert Tony Drakeford called for caution. "My first inclination from hearing these plans is to be suspicious," he said. "The problem is as soon as you hear the word park mentioned, I think of a manicured area that destroys natural wildlife. This could have the wrong effect altogether if they flatten wonderful natural areas to create pathways and recreation areas."