ROBBIE DINWOODIE and MICHAEL SETTLE

ATTEMPTS to drag Des Browne, the Scottish Secretary, into the independence referendum row were rebuffed last night as "laughable".

Angus Robertson, the SNP's Westminster leader, questioned what he saw as the lack of leadership being demonstrated by the Secretary of State given the "eerie silence" from the Scotland Office.

"Des Browne has been adamant in his opposition to a referendum," he said. "What does he think now? Does he agree with Wendy Alexander or is he behind Gordon Brown's decision not to back her latest big idea?"

The Moray MP added: "The Scotland Office was quick to wrest the Calman Commission from Scottish control. It is clear from Wendy Alexander and Gordon Brown's behaviour this week that the Scotland Office, the department meant to look after Scotland's constitution, is now completely irrelevant."

David Mundell, the Conservatives' shadow Scottish Secretary, also turned up the pressure on Mr Browne, saying in a letter how surprised he was to learn that he had "refused to appear on Newsnight Scotland each night this week to explain your and your government's position on an independence referendum.

"Given the obvious schism which exists between the Prime Minister and his leader in the Scottish Parliament, Wendy Alexander, over the issue, it is extraordinary that in your role as Secretary of State for Scotland your voice has not been heard."

However, last night, the Scotland Office hit back, saying the opposition parties' attempts to involve Mr Browne in the referendum row were "laughable".

A departmental spokesman said: "When the Prime Minister speaks, he speaks for the government. There is no need for the Secretary of State to come out and endorse that."

He added that the PM's spokesman had made clear the UK Government had no plans at Westminster to bring forward an independence referendum: "This is a Unionist Government. That's why the Calman Commission was established to look at strengthening devolution.

"Wendy Alexander has taken a tactical decision with regard to the proposal by the SNP Government. That falls within her sphere of influence as leader of the Labour Group in the Scottish Parliament."

However, last night, Sir Menzies Campbell, the former LibDem leader, argued that the week's events had "undoubtedly undermined the Calman Commission".

He said: "It's going to take all of Sir Kenneth's commitment and skill to maintain the credibility of his commission following Labour's astonishing conversion to an independence referendum."

Earlier this week, Sir Kenneth, who chairs the commission, felt it necessary to write to the 14 members of the body, reassuring them that they still had a job to do. He said: "The party leaders and UK Ministers remain fully behind the commission."

Mr Brown was yesterday on government and party business in Cornwall, which included a visit to the Eden Project, but Harriet Harman, the Commons Leader, insisted the UK Government was not confused over the independence referendum issue and was strongly pro-Union.

When asked repeatedly if she agreed with Ms Alexander's "bring it on" line, she referred to the work of the commission, declaring there was "no fundamental split" in Labour ranks.

The Scottish Labour leader received support from one unexpected quarter: Lord Forsyth, the former Conservative Scottish Secretary, backed her call for an early independence referendum.

After a Yougov poll gave the Tories a 26% UK lead, putting Labour on just 23 points, its lowest-ever showing, the SNP pointed to the Scottish sample - albeit only 141 respondents - putting it on 32%, Labour on 26%, the Tories on 21% and the Lib Dems on 13%.

Nicola Sturgeon, the SNP's deputy leader, said: "Wendy's U-turn has helped put Labour into a crisis north and south of the border and put Labour's support at its lowest levels since 1918. Many Labour MPs' nerves will be rattled as the effect of Wendy Alexander's U-turn and Gordon Brown's unpopularity hits home."

Jackie Baillie, Labour's shadow minister for parliamentary business, savaged the SNP over reports that it could work with a David Cameron government.

"SNP votes ushered in the Thatcher Government in 1979. Clearly, the Nationalist leopard hasn't changed its spots," she insisted.

However, a source close to the First Minister made it clear there would be no formal SNP-Conservative pact should Mr Cameron win power at Westminster; rather, the Scottish Government would "approach every issue case by case" to get the best deal for Scotland.