The latest poll, by TNS, added to the mood of urgency and anxiety for Labour and the coalition government, disclosing that support for independence has jumped six points in a month, pushing the yes vote to 38%, a single point behind no at 39%.
With no campaigners saying they were baffled by the sudden surge in support for yes, Brown came out of semi-retirement from frontline politics to lead Scottish Labour's drive to regain control of the independence debate with further proposals to devolve powers to the nation and inject some previously absent passion.
Addressing Labour voters at a former miners' club near Edinburgh, the former prime minister said Scotland's voters deserved to have demands for greater autonomy addressed urgently by Westminster, in an intervention immediately backed by David Cameron and Nick Clegg, and given the blessing of Ed Miliband.
Speaking on the first leg of a cross-country speaking tour over the next 10 days, Brown said: "What people are looking for is a timetable, a plan, a mechanism for delivery and a clear idea of what would happen after a no vote."
Insisting "the status quo is no longer an option", he said that "the choice is now between irreversible separation, or voting for a stronger Scottish parliament. We are talking about a big change in the constitution. It's like home rule in the UK. We would be moving quite close to something near to federalism in a country where 85% of the population is from one nation. Change is in the air and change is coming."
In language that reflected the sudden urgency of the late stages of the campaign, Brown said he had entered the debate at this point because "this is a referendum for 50 to 100 years ahead. We are not making a decision about ourselves. We are making a decision for the children of Scotland."
Scottish National party (SNP) sources claimed Brown's appeal across Scotland was patchy and diminished, adding that Scottish Labour campaigners failed with the same tactics when they belatedly reacted to a surge in SNP support in the 2011 Scottish parliament elections.
Yes campaign leaders have carefully avoided any triumphalism after the positive poll findings; a further poll for Yes Scotland by Panelbase suggested the yes vote was still four points behind no, adding to their caution.
But the yes campaign's growing confidence was nevertheless becoming apparent. The SNP deputy leader, Nicola Sturgeon, said: "I don't think there's any doubt at all the momentum is with the yes campaign but there is no sense of our campaign taking anything for granted."
Brown revealed that Labour wanted to see legislation put before the Commons a few weeks after Christmas. "Quite simply, Scottish voters deserve to know to the fullest extent possible about how new powers as ambitious as possible will be delivered as soon as possible within the UK. So we are demanding a tight timetable with tough deadlines and streamlined procedures."
He said that under the 12-point plan the coalition government would set out the options for devolution no later than the end of October. "Heads of agreement" would be published by November, after consultation with civic society, leading to draft clauses for legislation as the new Scotland bill.
The Brown proposals came a day after shares in Scottish banks and companies were hit on Monday. The pound also fell in value again, prompted by a weekend YouGov poll that said the yes campaign had recorded its first narrow lead.
Both Downing Street and the Liberal Democrats were consulted by Labour on its proposed timetable, and welcomed what they described as "Gordon Brown's initiative", adding the other Scottish unionist party leaders would say more on Tuesday. Cameron, aware of his limited appeal to Scottish voters, is taking a back seat, despite the momentous stakes, and will not travel to Scotland until next week, leaving his predecessor in No 10 to see if his standing with Scottish voters can save the 300-year-old union.
Miliband underwrote Brown's pledge, saying: "If we win the general election we will move with the utmost speed in our first Queen's speech to enact this legislation. It is Scottish Labour who have drawn up a timetable and a plan for a new Scotland Act. A Labour government will deliver it."
Labour wants the Scottish parliament to control and set Scottish income tax rates up to 15p in the pound and control all housing benefits in Scotland, worth another £1.7bn. The Tories and Lib Dems want to give Holyrood control over all Scottish income tax. Brown said he was confident that the Tories, Labour and Lib Dems could come to agreement on extra powers.
Brown also wants Holyrood's independence to be guaranteed by act of parliament, to fend off accusations that Westminster can control or veto its actions, with greater devolution of power to local councils.
Brown has been enlisted, or volunteered, after the latest polls confirmed voters are defecting in large numbers to support independence, bringing Alex Salmond's nationalist government and the wider independence movement to the brink of an unexpected victory. YouGov suggested on Sunday that a third of voters who backed Labour in the 2011 Holyrood elections would vote yes on 18 September. TNS put the figure at 24%. It said that among those certain to vote, no and yes were tied on 41%, but the long-term trend for TNS implied undecided voters were moving to yes.
But there was confusion in Labour's ranks after the shadow chancellor, Ed Balls, appeared unaware of the cross-party talks on an agreed devolution timetable, or that Labour could agree a deal on some extra powers before the 2015 general election.
Balls said he had had no talks with either George Osborne or Danny Alexander, the Lib Dem chief secretary to the Treasury, on a joint devolution; the only talks he knew of were internal Labour discussions about putting extra devolution in the 2015 general election manifesto.
"More widely, we're not planning on negotiating the first Queen's speech of the next Labour government with David Cameron and George Osborne," he said.TNS said the only age group where the no vote was in the lead was among those over 55 – mirroring YouGov's findings on Sunday. Among all voters aged under 55, there was a nine-point majority for yes.
The pace of campaigning is reaching a climax: Yes Scotland has booked 334 billboard sites in Scotland, distributing 4.9m campaign papers and leaflets to its campaigners, while Better Together, for the no campaign, has booked 200 advertising sites and is sending 4m leaflets to voters this week.
The Scottish leaders of the three main UK parties will set out the full timetable for extra devolution powers at a joint press conference in Edinburgh on Tuesday, with Brown's proposals expected to be very close to the final deal.
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