Politicians across south London have pledged to fight for an “essential” rail service - despite warnings the Government will not listen to their demands.

They want Thameslink services linking Wimbledon, Sutton and Streatham to the city to carry on travelling north to Luton when the route is overhauled in 2016.

But a spokesman for Network Rail said he expected the Government to stick to its plans for these trains to terminate at Blackfriars - and warned a through service would mean track layouts that reduced overall capacity on the network, which connects fifty stations in and around London.

Those who have promised to lobby the Government include Wimbledon MP Stephen Hammond, who said: “I will do everything I can to ensure that at best some of the service is a through service.”

He said after talks with ministers the Government had promised not to finalise timetables until it had investigated sending trains north of Blackfriars.

Carshalton and Wallington MP Tom Brake said Thameslink was an essential service for his constituents. He said: “In Sutton we miss out on some of the big projects like Crossrail, so it’s only fair that commuters from my patch should benefit.”

A spokesman for Streatham MP Chuka Umunna said passengers from his area should be consulted as soon as possible on changes to the “really important” service. He said: “Users haven’t been given all the information.”

The Thameslink expansion is set to bring another 100 stations and bigger trains into the network.

A spokesman for Network Rail, said: “Our current expectation is that these services will terminate at London Bridge or Blackfriars stations.”

“Although this would mean that there would be no ‘through’ trains to stations north of Blackfriars, passengers would benefit from a significantly improved service because of the increased capacity and an onward service of up to 24 trains each hour through central London and beyond.”