Alex Salmond yesterday admitted that a second independence referendum would not be held for "a generation" if the SNP failed to secure a "yes'' vote first time around as he conceded more ground in an attempt to secure a coalition with the Liberal Democrats.

The SNP leader also said he had no problem with the idea of a multi-question referendum which would also ask voters if they wanted the Scottish Parliament to have more powers rather than full independence.

He also predicted turnout on May 3 will exceed 60%, defended his party's plans to replace the council tax with a local income tax, outlined his position on Scottish membership of the euro and told how a team of academic advisers would set his government's economic policy.

And any attempts by Labour and the Liberal Democrats to form a unionist coalition to keep the Nationalists from power would amount to "an unpopular front", Mr Salmond said.

He made his comments at a debate organised by The Herald and sponsored by the Scottish Chambers of Commerce.

Mr Salmond's comments on a second referendum were in direct contrast to comments he made at the launch of his party's manifesto earlier this month.

At that time Mr Salmond appeared to open up the possibility of another referendum if the SNP was returned to power at Holyrood.

The strategy brought attacks from opponents that Scotland would face a "never-endum" resulting in a long-running political stalemate.

But speaking yesterday Mr Salmond insisted Scots would not face repeated visits to the polls if they initially vote no''.

"You can only have another referendum if the people so allowed in a future General Election," Mr Salmond told a 200-strong audience at the Mitchell Library in Glasgow.

"In my view it's a once in a generation thing. There was a referendum on devolution in 1979 and then the next referendum on devolution was in 1997 and that seems to me to be the overwhelming likelihood."

Mr Salmond was in confident mood during the debate, his demeanour undoubtedly explained by his party's continuing lead in the opinion polls.

Acknowledging that a coalition, almost certainly with the Liberal Democrats, would be his ideal scenario should the SNP be the largest party following the election, Mr Salmond said he would be "as flexible as possible" on the subject of an independence referendum.

"A multi-option referendum is at least in principle possible," he said.

"As long as the concept of independence is on the ballot paper, that fulfils our obligation, not just to our supporters, but also to the people in terms of what we are arguing in this election."

Mr Salmond also suggested that any coalition between Labour and the LibDems in the event of the SNP being the largest party after the election would be undemocratic.

He said: "If we had the circumstance where the SNP emerged as the leading party, then I think it would be incredible if there was a teaming up to shut the SNP out of power. In Spanish politics they used to have the Popular Front - well that would be the unpopular front.

"The idea of keeping somebody in power when they have been rejected by the electorate would, in my view, be an incredible one."

The SNP leader said that with so much at stake on May 3, he was in no doubt that turnout would be far higher than four years ago, when barely half the electorate went to the polls.

"I think it will be much higher - 60% at least," he said.

The SNP's plans for a local income tax to replace the council tax has been one of the most keenly debated policies of the campaign, with Labour attacking it on an almost daily basis.

Mr Salmond yesterday insisted it was a fairer system which would leave the vast majority of Scots better off.

He said that since the council tax was introduced, countless constituents had complained to him about how they were struggling to pay their bills. "The council tax is a system of taxation which is unfair because it can be unrelated to people's ability to pay," he said. "To substitute it for a type of taxation which is related to ability to pay is inherently fairer."

Appointing a council of economic advisers to set an annual growth target is also a key plank of the SNP manifesto.

Mr Salmond said the idea had worked well in America, where it was first introduced by President Truman.

Over the last 10 years, Scotland's annual economic growth has been around 2%.

Mr Salmond said it would be the job of his advisers, in an independent Scotland, to help take that to 4% - the average growth rate of other small, independent European nations.

"This seems to me to be a good target to have," he said. "The idea of having a target is to focus institutions so they achieve that target."

Responding to reports that oil revenues are set to fall, casting a doubt over the SNP's long-term economic thinking, Mr Salmond remained upbeat, predicting that supplies could last for another 40 or 50 years.

He also said Scotland should follow the example of Norway, which has set up a capital fund from oil revenues worth £300bn to fund public services for generations to come.

Mr Salmond also defended his party's plans to stick with sterling, at least in the short term, should Scotland gain independence.

He said such a move would help to ease any future transition to the eurozone, which he said he was in favour of if the economic conditions were right.

However, the final decision on whether Scotland adopted the euro would also be put to a referendum, he said.

Some critics have suggested that a Scotland which was out of the UK but in the European Union would be no more independent than it is now.

But that charge was dismissed by Mr Salmond, who mounted a stout defence of his party's old mantra of "independence in Europe".

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"If Scotland were an independent country within the EU, then we would control 99% of our revenue, with the remaining 1% being our Vat contribution," he said.

"Currently, we control 12.5% as a devolved government; 99% control is independence in an inter-dependent world."