The SNP have accused the UK Government of burying a key Whitehall report about a potential extension of the new HS2 (high speed rail) scheme into Scotland.

Scottish ministers have written to the Transport Secretary Patrick McLoughlin a number of times to press for the findings to be made public. It will not be published before the General Election.

The row comes amid suggestions the SNP would try to make the future of the £50 billion rail scheme a key battleground if there is a hung parliament after May.

Former First Minister Alex Salmond has said that HS could form part of the SNP's demands as part of propping up a minority Labour government if there is a hung parliament in May.

The SNP has now criticised the Conservative-Liberal Democrat government for not releasing the report before the start of the election campaign.

The civil service has new entered the official 'purdah' which restricts what can be published.

Patrick Grady, the SNP candidate in Glasgow North, said: "This report being kicked into the long grass until after the general election simply isn't good enough".

The Department for Transport (DfT) says that the report is now with ministers who are considering the next step.

A spokesman said that the findings would be made public "in due course".

The report into possibly extending HS2 into Scotland was initially launched with great fanfare by the Lib Dem transport ministers.

It had been thought that its findings would be available before the independence referendum.

Delays meant it was not given to Coalition ministers until the end of last year and they have been aware of the report's conclusions since December.

Last month Mr Salmond suggested that the SNP could call for work on an HS2 extension to begin in Scotland, if a Labour minority government was in power after May.

The ex-SNP leader suggested the idea when asked to provide an example of what the SNP might do if a Labour chancellor refused to alter a Labour Budget to meet the SNP's demands.

Mr Salmond suggested his party could propose amendments to the Budget, saying: "Instead of this very, very slow train coming up from London, I think we should start it from Edinburgh/Glasgow to Newcastle and I put that down as a budget amendment."

"It would have substantial support from the north of England and other parties and would carry the House of Commons," he went on to predict.

Last month a group of peers warned that other parts of the UK, including parts of northern Scotland, must not lose out as a result of the £50billion rail project.

A DfT spokesman said that Scottish rail passengers would benefit even if HS2 was not extended north of the border.

The current plans for the line to run to Midlands and then the north of England are forecast to shave time from the rail journey between Glasgow and London.

A DfT spokesman said: "Advice prepared by HS2 Ltd to identify broad options for high speed and upgraded railways to the north of England and Scotland has been completed on time and is now with ministers, who are considering next steps.

"This advice will be published in due course."