The political debate on Scotland has focused on which party will maintain the country's share of UK spending.

Nationalists have accused Labour of "having something to hide" over its plans for Scotland's future budget.

While Labour in turn has said the Conservatives would reduce spending north of the border.

Scotland secretary Alistair Darling on Monday released a letter to his Conservative opposite number, Peter Duncan, questioning whether the Tories would stand by Labour's block grant funding for the Edinburgh executive.

Darling said that from 2008 planned Tory spending cuts in Westminster would result in lower spending by the Scottish administration as a result of the Barnet formula which divides spending allocations between the home nations.

"Previously you have claimed that spending would be the same in Scotland under Oliver Letwin as it will under Gordon Brown," wrote Darling.

"It is clear that the so called 'Letwin guarantee', if it is to be believed, is only for two years and after that Barnett will apply to your UK wide cuts. 

"It would be helpful if you would now tell us which schools, hospitals and police services in Scotland would be cut under the Tories."

Over the weekend, the SNP said both Number 10 and the Treasury had refused to release information held by the government on its future plans for the Barnet formula.

"The web of secrecy about Labour’s plans for spending cuts in Scotland is spreading," said Scottish nationalist leader Alex Salmond.

"Somewhere in Whitehall a plot to cut Scottish spending exists.

"The people of Scotland have a right to know what Labour plans for Scottish spending after the election.

"Empty assurances are not good enough at this stage. Material exists on plans to scrap or change Barnett. That we know.

"Labour must now publish these papers or be damned by voters in Scotland."