Alex Salmond is pinning his hopes for an independence referendum on the next Westminster election, believing the outcome could shift entrenched opposition to the idea among Holyrood MSPs.

The First Minister will tomorrow set out his plans for a "national conversation", to build support for more powers at the Scottish Parliament.

It will be followed by a series of events around every part of Scotland but that use of executive resources faces opposition criticism.

The dialogue is intended to appeal to the Scottish public over the heads of the majority of MSPs who oppose a referendum. It is also a means of exploiting divisions within the Liberal Democrat and Conservative parties, who are both considering further devolution.

But in the face of firm opposition among MSPs at Holyrood, the SNP is pinning its hopes on the next Westminster election being the catalyst for a sea change in political opinion.

That election is most likely in May 2009 but there is growing pressure on Gordon Brown to call an election before then, while David Cameron's Tories are in disarray and the new Prime Minister is riding high in the polls.

Yesterday, there was further evidence of Labour's UK-wide poll lead. A YouGov survey of voting intentions put Labour on 42%, Conservatives on 32% and LibDems on 14%.

However, the pressure on Mr Brown is very different in Scotland. A poll of Scottish opinion last week made SNP "first choice" for 48%, Labour had 32% and LibDems and Tories were on 8% each.

According to a source close to the SNP leader, referendum support from 50 MSPs, 15 short of a majority, does not derail the pre-election intention of a 2010 referendum.

"We see the national conversation leading logically to a parliamentary process," he said. "By then, a lot of things can change which could be significant for Scotland".

He cited Wales, where Labour is not only in coalition with Plaid Cymru but committed to support a "yes" vote in a referendum on additional powers for the Cardiff Assembly. He also highlighted a report yesterday saying Scottish Tory leader Annabel Goldie has been told by Lord Forsyth, a Conservatives former Scottish Secretary, that she is making "a huge mistake" by refusing to back a referendum. As a firm unionist, Lord Forsyth believes the Tories could call Mr Salmond's bluff, force a quick referendum, and gamble that voters would say "no" to independence.

According to the executive source: "It's a fluid situation. The catalyst for that could be the next election. There's nothing like an election to change a party's position. It could be a wake-up call to Labour, to the LibDems, or the Tories could listen to what Lord Forsyth is saying."

However, a spokesman for Miss Goldie responded to Lord Forsyth: "A snap referendum is not on the agenda and we don't accept that would be the end of the argument.

"There are international comparisons that show that is not the case. What is required is stability, and we have that so long as the unionist parties stick to their guns".