The link, which would compete with low-cost airlines, would aim to offer a greener and more comfortable alternative to flying.

A Nationalist-led administration would enter into early talks with the UK government and offer to pay up to 10% of the costs of constructing the rail line across Britain.

The move is seen as an effort to seize the initiative from Labour after reports that a government-commissioned study by Sir Rod Eddington, the former British Airways chief executive, will reject a new north-south high-speed line.

SNP MSPs also believe it would counter attacks from Gordon Brown and Jack McConnell that a nationalist government would tear Britain apart.

Rather than adopt an isolationist strategy that pits Scotland against England, the nationalists want to emphasise that they recognise the economic importance of working in partnership with the government in Westminster.

Fergus Ewing, the SNP shadow transport minister, said a journey time of three hours would give passengers a powerful incentive to take the train and reduce pollution by removing the need for some of the 100 daily flights between Scotland and London.

He said: “It would also allow Scotland to forge closer social and economic links with our neighbours in England. The Treasury in London used Sir Rod Eddington to investigate the feasibility of this route but the leak of his apparent conclusion is that Scotland would be cut off — and any high-speed rail link would serve only England. He said that the link should stop at the north of England.”

Under the SNP strategy, a Nationalist-led coalition in Edinburgh would meet the cost of new track in Scotland if the UK government paid for the required new railway in England.

The Treasury estimates that the rail link could cost £33 billion to construct but Iain Coucher, deputy chief executive of Network Rail, believes a high-speed rail network could be built for about £15 billion.

“If you can get around 70% to 80% of people who travel from London to Edinburgh or Glasgow on the train then you are also talking about raising significant income,” Coucher added.

Adrian Lyons, director-general of the Railway Forum, a think tank and lobby group on the railway industry, said a high-speed rail link would bring massive economic benefit to Scotland and prevent its population from declining.

“There is plenty of evidence across Europe that transport links halt decline. For instance, with the high-speed link between Seville and Madrid, people can live in Seville and not feel cut off from Madrid,” he said.

“Even if Scotland’s share was to be 20% of the cost it would be worth it in terms of the social and economic issues.”

The SNP favours a link that would connect Scotland to Birmingham, London and Manchester. This is likely to be cheaper than a network that would include Manchester, Leeds and Newcastle because it would require fewer miles of new track.

John McCormick, chairman of the Scottish Association for Public Transport, welcomed the SNP’s support for the link and accused Labour of inaction.

“This has been on the agenda for years but the Labour party has not done anything about it. Although a report is due out soon, there is the impression they are not committed to doing anything and I believe the Treasury is trying to stop anything happening on it.

“Air transport is a growing source of atmospheric pollution and if we do not do something about this the environmental targets will never be met.”

Last month the Conservatives raised the prospect of building a 360mph magnetic levitation, or Maglev, train service in the UK.

George Osborne, the shadow chancellor, said that high-speed train links between Liverpool and Manchester, Glasgow and Edinburgh, or London and its airports would bring huge benefits to Britain.

However, confidence in Maglev technology was shaken earlier this month when a collision involving a high-speed magnetic train on a monorail killed 23 people in Germany.