HS2 is merely “a political trophy project” according to Lord Mandelson, who spoke against the project in the House of Lords yesterday.

He said there were dozens of transport projects that could be implemented for the price of HS2, and disputed the benefits of faster journeys.

But former Labour minister Lord Rooker said it would be “inconceivable to withdraw support” from the project.

Lord Mandelson, who is still an influential figure in the Labour Party, said: “I have been an ardent pro-railway supporter all my adult life. But it is precisely for that reason that I do not support HS2. I think the sheer cost of it will suck the very lifeblood out of the rest of the country’s rail system.

“Frankly there was too much of the argument that if everyone else had got a high speed train we should have one too – regardless of costs and alternatives. If this goes ahead we will see a shrinking of the rail network in this country and that should be the very last thing pro-rail supporters would want to see.”

Lord Rooker said: “The Labour government started this project and it will be inconceivable to withdraw support. I am getting cheesed off listening to ex ministers swanning around the political salons pouring cold water on this project.

“I urge the shadow cabinet not to quit on the project but to fight for it. I urge HS2 to get its communications and operations a bit more transparent.

“In the days of the great engineering projects approved in private bills by this Parliament the likes of Brunel and Telford got on with their vision and they won through in the end and thank goodness they did.

“They would be ashamed and astonished to see us today – a scrimping nation getting by, or at least we think we are.”