The Prime Minister was urged yesterday to go further than his remarks about more fiscal autonomy for Holyrood and pledge that a review of Scottish devolution being undertaken by the Calman Commission would not be used to claw back any powers to Westminster.

Gordon Brown had said in Glasgow that while the Scottish Parliament was accountable for its spending it had no control over the size of its budget, which was not linked to the success of the economy.

"That is why we asked the commission to look carefully at the financial accountability of the Scottish Parliament and this is a critical part of Calman's remit," he had claimed.

Mr Brown was said to be surprised yesterday that his remarks at a CBI dinner in Glasgow had been interpreted as a U-turn. An aide said: "This is exactly what we started out by saying when we established Calman, but the principle has to be what is in the best interests of Scotland."

This did not prevent the SNP seeing it as an about-turn, with Westminster leader Angus Robertson saying: "Brown's conversion to tax powers for the Scottish Parliament is welcome but it must be accompanied by a clear statement that he has dropped the ludicrous suggestion that powers could be taken away from the Scottish Parliament.

"It is amazing the impact a lost by-election and the prospect of a challenging contest in Glenrothes has had on the Prime Minister.

"Not only has he suddenly decided to visit not just Scotland, but Glenrothes in particular, we are seeing the impact of SNP success on Labour's failing UK Government. As Labour panic over another by-election it is clear that when the SNP does well Scotland does well."

Mr Robertson added: "In Glasgow East we asked people to send a message to Gordon Brown, to tell him to change his policies. That message won a freeze in the 2p rise on fuel duty and a conversion to tax powers for the Scottish Parliament.

"Now it's for people in Fife to secure a fair deal on energy prices and soaring fuel costs."

New Scottish Liberal Democrat leader Tavish Scott told a gathering of his party's parliamentarians and candidates in Edinburgh yesterday: "Dithering and indecision are in Gordon Brown's DNA. If this is a genuine conversion to the Liberal Democrat plans for a stronger Scottish Parliament, then he must back his words with action.

"The people of Scotland will judge him harshly if these turn out to be weasel words just to get through a difficult by-election. Scotland's constitutional future is too important for word games and spin from the Prime Minister or First Minister."

He added: "Will the Prime Minister back our calls for Scotland to raise the money it spends? Will he back more powers over the taxes we need to influence the Scottish economy and tackle the challenges people in Scotland face?"