Fears have grown over the future of the line after both South Gloucestershire Council and Bristol City Council withdrew the £150,000 subsidy for the hourly Severn Beach to Bristol service. The Department for Transport and the Government Office for the South West has picked up the bill to carry on the funding.

Train operator First Great Western, which has taken over the franchise to run the service from Wessex Trains, has pledged to keep the Severn Beach line open.

But Transport secretary Alistair Darling last year said the Government would not subsidise community railway lines beyond 2009 unless they were able to attract more passengers. Ms McCarthy, a Labour MP, will today table a motion to the House of Commons calling for the line to be protected.

The Post reported last week how Bristol West MP Stephen Williams had called on fellow politicians to back a petition to exert pressure on the Department of Transport.

The Liberal Democrat's motion stated that the line "carries thousands of commuters per week".

It adds: "This House calls on the Government to ensure that this valuable line is maintained for the benefit and enjoyment of the local community and visitors."

Union leaders have also now come out in support of the Severn Beach line.

The Rail Maritime and Transport Union has warned that it could close altogether, and is to lobby the city council.

General Secretary Bob Crow said: "The Severn Beach line needs more services, not fewer."

Julie Boston, campaigner for Suburban Bristol Railways, said there was enough demand for two services an hour on the line.

She said: "It is ridiculous that places like Patchway only have one service an hour. They could run once every half an hour and feed into services going to Cardiff, Bath and Swindon."

The railway runs from Temple Meads through Lawrence Hill, Montpelier, Redland, the Clifton Downs, Avonmouth and Severn Beach.