DOUGLAS FRASER and ROBBIE DINWOODIE Moves towards a governing coalition gathered pace rapidly yesterday as the SNP held informal talks with Greens and Liberal Democrats.

Formal talks between the Nationalists and Greens are due to open this afternoon, hosted by the civil service, and marking a historic first for both parties - neither of which has held power before.

However, progress in talks with LibDems stalled last night after the party's MSP group in Edinburgh refused to give ground in their opposition to a an independence referendum. Party leader Nicol Stephen made clear he would prefer being in opposition to conceding that point, "leaving the ball in the SNP's court". The impasse is a classic negotiating stand-off, in which both sides wait for the other to concede first.

The post-election moves followed the Nationalist offer of a constitutional convention, intended to appeal to LibDems. The convention could be used to set aside disagreement between the two parties on the referendum plan, and would pose a dilemma for Scottish Labour on whether to join or not, having criticised the SNP and Tories for refusing to join in the first home rule convention that led to devolution.

It would give LibDems time and space to work up their own plans for devolving further powers to Holyrood, and would still keep a referendum within Nationalists' sights.

However, it could be the means for postponing a referendum beyond the next four years. Although Mr Salmond wanted to hold a vote by the next Holyrood election in 2011, he faces a clear majority of MSPs opposed to that.

Following a telephone discussion late on Saturday between Mr Salmond and Mr Stephen, the smaller party moved to rule out any prospect of a return to a governing coalition with the Labour Party. Mr Salmond had been keen to rule out the feared prospect of an anti-Nationalist alliance, including Labour, LibDems and Tories. LibDem campaign director Tavish Scott left no doubt about that possibility during a TV interview yesterday.

The announcement ran counter to reports that Sir Menzies Campbell, LibDem leader at Westminster, had agreed with Labour's next leader, Gordon Brown, that they should work together to keep Nationalists out. Both MPs are concerned about leading their parties into the next Westminster elections if Scotland is run by a party committed to removing their seats from the Commons.

Yesterday, Mr Salmond cleared the way for formal talks with the Scottish Green Party whose two MSPs he would need, along with the LibDems, to secure majority. The SNP won 47 seats last week with LibDems on 16 and two Greens - equalling the 65 required for majority.

Following informal discussions with remaining MSPs Robin Harper and Patrick Harvie, there was agreement that both sides are committed to a rejection of any new nuclear power plants and to annual targets for reducing carbon emissions, leaving no barriers to further talks.

However, there are more difficult issues for the parties to address around Green opposition to the M74 extension through Glasgow, the Aberdeen relief road and aviation expansion.

An SNP leadership source said: "The SNP have come a long way to recognise the concerns and the principled positions, saying we can find a middle way, being co-operative, progressive and constructive to find an agreement everybody can be happy with."

He added: "We'll need movement. The SNP have moved, and are moving. We hope others will show the same flexibility. The mood of the country is for a change of government and a new way of doing things. People are looking at what we can do rather than what we can't do together."

Mr Salmond could find resistance within his party to any delay in the referendum plan beyond the 2011 election. A hardliner in the SNP MSP group yesterday refused even to consider a delay, turning the pressure back onto LibDems, with the claim that polls show LibDem supporters back a vote on the future of the constitution.