The SNP promise to hold a referendum on independence was yesterday called into question, as Alex Salmond opened up room for coalition negotiations after the May election.

The SNP pledge to hold a referendum on independence - as early as this year - was yesterday thrown into doubt.

Alex Salmond opened up room for coalition negotiations after the May election, saying the choice would only be put once people had a chance to debate and digest the proposals being put forward.

The SNP leader said the party remained determined to have a referendum within the four-year term, but previously he had promised to move swiftly to legislation for a referendum. Yesterday's change should give him more room to compromise with other potential coalition partners - Liberal Democrats in particular - on when that might be and under what conditions.

He said: "Initially, we'll publish a white paper, so that people understand the proposal, can see the proposal published, have time to discuss, debate and digest it. But within the four-year term, if the people speak in favour of a referendum, then a referendum there shall be."

He had previously said the bill would be introduced within 100 days, and his party has published a bill to illustrate how simple it could be.

However, he dismissed the sample bill yesterday. "There is a world of difference between being an opposition saying this is what we're talking about' and being in government."

Mr Salmond went on to explain further: "I'm not going to argue over the principle of the referendum, but what we have to do is have some flexibility in the timing, so we'll introduce the bill into the parliament when the timing is right."

The tactical change was described as "panic" by LibDems, while Labour's deputy campaign director, Lord George Foulkes, said Mr Salmond was "going soft and running scared because he has finally realised just how unpopular independence is".

The SNP cause received a substantial boost yesterday with the endorsement of the party and Mr Salmond by Crawford Beveridge, former chief executive of Scottish Enterprise who now works for Sun Microsystems.

"I believe independence could focus the minds of politicians to create the conditions for economic growth, which would translate to better jobs, higher wages and stronger communities," the business leader said.

He downplayed fears about Scotland running a deficit, saying many countries do so, and added: "Scotland is just as capable of running its own affairs as any country."

The argument for Holyrood having at least more fiscal powers has gained ground in the business community in recent months, while Labour First Minister Jack McConnell has expressed frustration that unionist business leaders are too reluctant to go public with their fears about separation.

There was mixed evidence yesterday on the prospect of Mr Salmond becoming First Minister, with one poll giving the SNP a clear lead, and another showing Labour increasing its share of seats.

A YouGov poll showed his party has a six-point lead on the headline question of constituency voting intentions, and a two-point lead on the regional vote.

On the constituency poll, the web-based survey put the SNP on 35, Labour on 29, LibDems 18 and Conservatives 13. On the regional vote for list MSPs, the SNP was on 32, Labour 30, LibDems 14, Tories 14, Greens five and both far-left parties on one.

Another poll, taken by ONS System Three, would see Labour gain two seats on its 2003 result. In face-to-face interviews, the opinion survey company has consistently found comfortable Labour leads, in contrast with other pollsters.

On the constituency vote, it put Labour on 38, the SNP on 33, LibDems on 14 and Tories on 11. On the constituency vote, it showed Labour with 33% support, with the SNP having 30, LibDems 16, Tories 13, Greens six and socialists three.