Gordon Brown yesterday conspicuously failed to back the call by Wendy Alexander and other political leaders in Scotland for Holyrood to be given more powers, particularly over tax.

However, a source close to First Minister Alex Salmond told The Herald last night that it was now clear the Prime Minister had conceded that the debate on the future powers of the Scottish Parliament had begun in earnest.

"He was forced into a significant concession in accepting that the debate on more powers for Holyrood is under way. This will stick in the throat of most Scottish Labour MPs," insisted the source.

At his monthly Downing St press conference, Mr Brown was asked directly if he was for or against what has become the cross-party consensus in Edinburgh for an extension to home rule.

He replied: "This is a debate about the responsibility and accountability of the Scottish Parliament for the use of resources it spends. This is a debate that has to be held at some point over the next few years about accountability for money spent. That's why we're looking at different ways in which that debate can happen but I'm not going to conclude the debate. It's a debate that should happen."

Mr Brown declared 2008 would be an "important year for the Union" but did not elaborate. He stressed: "It's important to remember that two-thirds of the people of Scotland voted in the last elections for the Scottish Parliament for parties that oppose separation; for parties that support the maintenance of the Union."

Ms Alexander, Labour's leader at Holyrood, marked a political watershed in her party's thinking on extending home rule when in November she said: "There is a desire in Scotland to walk taller rather than to walk out. Part of walking taller is that we should take more financial responsibility for our own affairs in Scotland. We should not let housekeeping bills get in the way of breaking the marriage but the housekeeping bills deserve to be looked at again."

She has set a cross-party commission involving the Conservatives and Liberal Democrats at Holyrood and Westminster on the future of devolution but it is known that some Scottish Labour MPs are deeply unhappy about it and believe Ms Alexander is "dancing to the Nationalist tune".

Last night, Angus Robertson, the SNP's leader at Westminster, claimed that the Prime Minister had made a gaffe at his monthly press conference, arguing that Mr Brown had "asserted that London rule was the preference in Scotland".

"Having lost the Scottish Parliament elections, Gordon Brown still doesn't seem to realise that people in Scotland want more decisions taken closer to home," declared the Moray MP.

"The majority of Scots voted in 2007 for parties committed to increasing the powers of the Scottish Parliament. Labour has been the last party to formally recognise the demand for further powers but they still don't trust the people to decide."

Mr Robertson added: "The SNP believes the people should have the choice and we are confident, with the rising support for independence, that Scotland will choose independence."