Leading politicians from Holyrood and Westminster will gather behind closed doors in London today for their first meeting to discuss the prospect of giving the Scottish Parliament more powers.

Wendy Alexander, Annabel Goldie and Nicol Stephen, the respective leaders of the Labour, Conservative and Liberal Democrat parties at Holyrood, will privately meet their London counterparts in a room at the House of Commons to discuss how the proposed constitutional commission on devolution should be established and to underpin Unionist opposition to the independence policy of the Nationalists.

Last night, a source close to Des Browne, the Scottish Secretary, told The Herald: "It's critical at the moment for the Unionist parties to work together to demonstrate the fact that the settled will of the Scottish people is for devolution.

"They voted for that in a referendum, at the last election in May and every opinion poll shows they are against independence. The meeting will also show the need for parties to work together to demonstrate that the SNP is a minority party when it comes to separation."

He added: "The meeting is also important as a way of finding a process in which the commission can be looked at in a thoughtful way rather than making it a political football to be kicked around the Scottish Parliament."

Mr Browne met the three Scottish Unionist leaders in Scotland in November to discuss the idea of the commission shortly after MSPs voted in favour of setting it up.

This lunchtime in a room in Portcullis House, a plush Commons annex, he will join David Mundell, the Conservatives' Shadow Scottish Secretary, and Alistair Carmichael, the Liberal Democrats' spokesman on Scotland, for talks with their Holyrood colleagues. The grouping has already been dubbed the "Scottish Six".

Mr Mundell said: "The commission is an incremental process but this will be an important first step to discuss details about how it will operate and to get it up and running in the near future."

He added: "This is a very important initiative, which the Conservatives are committed to. David Cameron is committed to it. The fact that it is being held in London shows that this is not just a Scottish initiative but a UK initiative."

However, the SNP sought to rubbish the meeting, claiming it "ignored Scotland".

Alasdair Allan, the SNP MSP, said: "It's ironic but perhaps appropriate that the London parties should take forward their constitutional commission idea for Scotland's future by getting on the shuttle to London.

"This process is entirely explained by the SNP's success and the Scottish Government's national conversation - the other parties' flight to London is fuelled by the SNP."

Claiming that Scottish political trends were "all going in the direction of the SNP" and that it was now more likely there would be a referendum on independence, Mr Allan added: "The task for the main opposition parties, who now all advocate more powers for the parliament, is to define exactly which powers they mean so that the option can then be included in a referendum ballot paper."

A Scottish Labour spokes-man hit back, saying it was not Scotland which was being ignored but the SNP. "Everyone in the room will have been elected by Scottish voters. The commission has a parliamentary mandate from Holyrood, unlike the SNP's national conversation," he added.

A Tory spokesman said: "Alasdair Allan's comments are nothing less that an anti-English rant that do him and his party no good at all."

The issue of more powers for Holyrood is now seen by all of Scotland's Unionist parties as the main means by which they will prevent First Minister Alex Salmond getting a second term in office.

Ms Alexander, whose brainchild the commission is, has called for a "more balanced home rule package" with Scotland possibly getting more powers on tax, welfare and transport.

However, there is great scepticism and anxiety about the move among some Scottish Labour MPs, thought to include Prime Minister Gordon Brown, that Ms Alexander and her colleagues are playing a dangerous game and dancing too merrily to the Nationalist tune.

  • The latest poll, a YouGov survey for the Scottish Daily Express, has put the SNP nine points ahead of Labour on the constituency vote. The party is three points ahead of its closest rival on the regional vote, the poll found, and 27% of respondents said they back independence in a referendum.