The First Minister delivered a bombshell announcement that the referendum on independence would probably not be a straight yes-no vote.
Instead, people would be asked to rank a series of options in order of preference – independence, the status quo or more powers for the parliament. This could mean independence being gained, even if only a minority rank it as first choice.
Critics immediately raised concerns because, on such a momentous issue, voters' second choices would become as important as the first, after the option with least votes was knocked out. In an extreme set of circumstances, independence could be achieved with only 26 per cent making it their top preference, if all the second-choice votes plumped for a break from the Union.
Mr Salmond's plan, which was announced at the launch of the second phase of the Scottish Government's "National Conversation" on independence, was met with howls of derision from political opponents who criticised a system that allowed the second-best, or least-worst, option to win through.
The Tories branded the plan "tripe", Labour said it was "the back of an envelope approach to Scotland's future", and the Lib Dems called it a "red herring".
The First Minister said that, although his preference was for a clear two-option question on independence, he would put forward a three-question referendum if that helped get the idea approved.
Earlier this week, the three main unionist parties set up a Scottish Constitutional Commission, under the leadership of Professor Sir Kenneth Calman, to try to find a way of increasing the powers of the Scottish Parliament while staying within the Union. They refused to look at independence as an option.
But Mr Salmond offered to put the results of Sir Kenneth's commission to the people as the third question on an independence referendum. "If we had a three-way referendum, the third option would have to be crystallised," he said, adding: "Scotland must have that choice; this must be available to the people of Scotland."
This was a clear ploy to try to embarrass the unionist parties: if they reject his overtures, Mr Salmond will accuse them of failing to put their ideas to the people; if they support his plan, he will secure the votes he needs to get the referendum approved by parliament.
Mr Salmond then explained how a three-question referendum would be decided.
He said: "People managed to get their heads around voting one-two-three in STV (single transferable vote) in the local government elections last year, so I think we want one-two-three in a three-option referendum. I'm pretty confident people in Scotland can manage three choices on a ballot paper."
Under this system, the first choice votes would be added up and the option with the least support eliminated. The second-choice votes from this third option would then be re-allocated and the option achieving the most overall votes would win.
When it was suggested to the First Minister that this was a "back door" way of getting independence – because it could be achieved with less than 50 per cent of first-choice preferences – Mr Salmond said: "This is not a back-door way. It is perfectly fair; it is a perfectly valid system of election that is used the world over.
"The idea that Scotland is not capable of engaging in a debate over the next two years, making crucial choices and decisions, is nonsense."
Annabel Goldie, the Scottish Tory leader, ridiculed what she described as an "absurd" referendum suggestion.
She said: "You do not decide the destiny of a country on the basis of the second-best or least-worst option. This is tripe – the wild words of a panicking man. Alex Salmond is clutching at straws for his minority whim.
"It may have escaped his notice, but you don't have a referendum to preserve the status quo – devolution is the status quo.
"Only if you want to take the place apart, as he does, do you require a referendum as a mandate for that wholesale destruction. His challenge is to win a mandate for independence at an election. The other three Scottish parties are in the business of making devolution work better – that's what Scotland wants."
Wendy Alexander, the Scottish Labour leader, said: "For a politician who talks about the need for a fair voting system, but then says there doesn't need to be a majority for independence, is frankly ridiculous.
"Once again it demonstrates the SNP's back-of-an-envelope approach to Scotland's future. Alex Salmond must be delusional if he thinks that Scotland will be happy to accept independence by the back door."
She went on: "The fact that poll after poll clearly shows Scots turning their back on independence must have started to register on the SNP. The penny has dropped that they will never get 50 per cent plus one, so he wants to change the rules.
"Braveheart this isn't – faintheart more like."
Nicol Stephen, the Scottish Liberal Democrat leader, added to the criticism, saying: "This referendum is a red herring designed to do nothing else than deflect attention from the falling support for independence."
The Scottish Government wants to hold a referendum in 2010, aware that if the opposition parties vote the plan out, the SNP will be able to go into the 2011 election accusing its opponents of denying the public its right to decide Scotland's future.
The First Minister did concede that, if he lost the independence vote, the SNP would not be able to put the question again for about 25 years, but he refused to accept that the decision would be "final". He said: "I believe this is a once-in-a-generation choice. It is not a final decision; it is not a final, final choice."
At the launch of the second phase of his "National Conversation", Mr Salmond met representatives of the trade unions, the business community, churches and voluntary organisations.
They then attended a series of seminars at Edinburgh University, each hosted by a Scottish Government minister. The bodies were encouraged to discuss the issues with their members and feed their views into the "National Conversation".
Among those there yesterday were Sir Muir Russell, convener of Universities Scotland; Matt Smith, Scottish Secretary of the public service union Unison, and David Watt, of the Institute of Directors.
Q & A:SALMOND'S MULTI-OPTION REFERENDUM
Q: What does Alex Salmond propose for a referendum?
A: The First Minister wants to put the question of independence to a referendum of the Scottish people. That would be his ideal solution, a simple, two-choice, referendum: independence, yes or no. But he says he is willing to compromise and include the prospect of more powers for the Scottish Parliament in the referendum.
This would give the electorate a choice of three options – independence, the status quo, or more powers for the parliament.
Q: Will Westminster get a say on the choice of voting system?
A: No, not unless the UK government attempts to hold its own referendum on independence first. If the Scottish Government decides to hold a referendum, and gets the support of the Scottish Parliament to do so, it will be for the Scottish Government to decide how to run it.
Q: How would the result be decided?
A: A three-way referendum could only be decided by voting preference. Rather than just putting an "X" against one option, voters would have to rank their preferences, with "1" for their first choice, "2" for their second and "3" for their third. When the first-preference votes are counted, the option with the lowest level of support would be eliminated and the second choices from this option redistributed to the other votes. The option which emerged with more than 50 per cent at the end of this process would be the winner.
Q: What needs to happen first before a referendum can be held?
A: The Scottish Government will introduce a bill at Holyrood, probably in 2010, which would pave the way for a referendum.
As it does not have a majority in the parliament, but has the support of the Greens and the independent MSP, Margo MacDonald, the SNP would need to persuade at least 15 opposition MSPs to support a referendum to have any chance of getting the bill through. At the moment, with all three main opposition parties opposed to a referendum, that looks unlikely.
If Mr Salmond does not get a majority in parliament, he will not be able to hold a referendum.
Q: The constitution is reserved to Westminster, so how can the Scottish Government even hold a referendum on it?
A: The SNP believes that, by asking the question in a way which deals with the Scottish Government, not the constitution, it can get around this problem. SNP managers believe that, if they ask the electorate for permission for Scottish ministers to start negotiating independence with Westminster, this will be allowed under the terms of the Scotland Act.
Q: Would they need to get the permission of Westminster to hold such a referendum?
A: They do not believe they would, if the referendum was carefully worded.
Scottish ministers believe they would be acting within the law – but this is merely the basis of their legal advice and this position has not been tested in the courts.
Q: Will the result have any weight if it only involves Scotland and not the rest of the UK?
A: Yes it would, but not because of any legal certainty, but because the UK government would not be able to resist the results of such a referendum politically. If Scots voted for independence in a referendum, it would give the Scottish Government the moral authority to negotiate independence.
All Prime Ministers since Margaret Thatcher have accepted the moral authority of such a decision.
It would not need the endorsement of the rest of the United Kingdom, because it would not involve the rest of the United Kingdom.
The Scottish Government would then start negotiating the end of the Act of Union between Scotland and the rest of the UK.
If successful, this would lead to Scotland leaving the Union, leaving the rest of the United Kingdom intact.
Analysis: Could three-way vote be a way of hedging bets to secure greater powers ?
REFERENDUMS are usually simply Yes or No affairs; voters are invited to approve or reject a proposal. But Alex Salmond, the First Minister, has long wanted something more complicated: a three-way choice between the status quo; devolution with more powers (perhaps whatever proposals emerge from the unionist parties' new commission) and independence. Now he has given us an idea of just how this might work.
With a Yes or No referendum, whichever option secures the most votes wins. But with three choices, the position is more complicated. Voters might be asked to vote separately for or against more powers and for or against independence – but then a majority might vote for both! Meanwhile, if voters are simply asked to say which they like most, none of the options may secure 50 per cent of the vote, leaving us unsure which has majority support.
Mr Salmond's answer to this problem is that instead of just saying which option they most prefer, voters should put them in order of preference, 1,2,3. This is what voters were asked to do in last year's local elections using the single transferable vote. If none of the options secures 50 per cent of the vote, the votes of those who supported the least popular option would be redistributed between the two remaining contenders in accordance with their second preferences. That way a clear winner could be found.
So say, for example, 41 per cent put independence first, 39 per cent devolution with more powers and 20 per cent the status quo, the votes of those who backed the status quo would be redistributed in accordance with their second preferences. If, say, three-quarters of them – worth 15 per cent of the total vote – backed devolution with more powers, and just a quarter – worth 5 per cent – independence, then devolution with more powers would emerge the winner by 54 per cent to 46 per cent, even though it was not the most popular option on the first preference vote.
But what if the option of devolution with more powers came third? Then it would be its voters' second preference that would count. Say, 41 per cent backed the status quo, 39 per cent independence and 20 per cent devolution with more powers. If then three-quarters of those favouring devolution with more powers backed independence with their second preference, independence would emerge the winner by 54 per cent to 46 per cent.
However, at the moment Mr Salmond's biggest worry must be whether independence can avoid coming third. A MRUK poll recently found 45 per cent in favour of devolution with more powers, 31per cent preferred the status quo or less, and just 23 per cent independence. Is it possible that Mr Salmond wants a preference vote so that the backers of independence are able to ensure devolution with more powers beats the status quo?
John Curtice is Professor of Politics, Strathclyde University