Campaigners and MPs are pushing for an unbroken 30 kilometre stretch of the River Crane to be opened to the public.
Action group Friends of the River Crane Environment (FORCE) has been trying to extend the reach of Crane Park east towards Twickenham Station and west in the direction of Feltham Marshalling Yards.
FORCE said £200,000 to enhance and open up the river-side stretch was given to Hounslow Council as part of a planning agreement with PostOffice Limited when it built the Jubilee sorting office, in GodfreyWay, Hounslow, six years ago.
"We are not sure what happened to the money but we know that a legal agreement between Hounslow Council and Railtrack fell apart over responsibility for two tunnels under the marshalling yards and the project stalled," said FORCE chairman Rob Gray.
Now Twickenham MP Vince Cable has called on Hounslow Council to unlock the land-ownership issues preventing public access, adding: "The problem is that the Hounslow stretch of the river is virtually inaccessible but also contains some of the most valuable nature reserve."
If access was granted the size of Crane Park, including Crane riverside, could suddenly jump from around 40 hectares to 98 hectares, giving it Metropolitan Park status and increased protection.
Network Rail, which owns a 400 metre stretch of the blocked route along the River Crane by the Royal Mail sorting office in Godfrey Way, said it was working with Hounslow Council on 'whether a footpath can be accommodated'.