Opponents of Scottish independence are to launch a last-ditch attempt to prevent the break-up of the United Kingdom as shockwaves continue to reverberate inside the pro-union camp following the first poll to put the Yes vote in the lead.
hancellor George Osborne has promised specific plans will be announced within days to enable Scotland to gain greater devolution in the event of a No vote, in an attempt to stem the tide of voters to the Yes camp.
With 10 days to go to the historic referendum, Ed Miliband and Gordon Brown will join up to 150 Labour MPs set to decamp to Scotland in a bid to step up campaigning.
Scottish First Minister Alex Salmond accused the No camp of "spiralling into self-destruction", but insisted independence supporters remained the underdogs in the battle for votes.
Yesterday's YouGov poll revealed that, of those who had decided, 51% backed the Yes campaign and 49% the No vote, giving a psychological boost to Mr Salmond and providing fresh evidence of a sharp drop in support for the UK over the last month.
A separate Panelbase poll put No ahead by 52% to 48%.
As the outcome of both surveys is within polling error, Scotland appears to be heading for a knife-edge result on September 18.
The figures intensified the jitters and recriminations within Better Together, with one prominent figure in the No camp admitting: "It has been pretty terrible run."
The campaign threatened to involve the Queen after a report yesterday that she was worried by the impact of a Yes vote on her constitutional status as Scottish head of state.
Reports suggested she may even be forced to appoint an Australian-style governor general to rule in her name.
But a Buckingham Palace spokesman said: "The Queen is neutral on all political issues. She always has been and always will be."
Both sides in the increasingly tense contest are set to pour massive resources into winning the support of a dwindling number of Don't Knows, who could hold the key to victory.
The SNP will today claim that only a Yes vote can protect the National Health Service from cuts by an ideologically driven Tory Government as it focuses on voters in Glasgow.
All Scottish Labour MPs have been instructed to spend this week campaigning, and they are expected to be joined by around 100 of their colleagues from south of the border.
Mr Osborne yesterday promised that detailed plans for the transfer of more powers to Holyrood would be set out this week. They will include extra powers over tax, spending and welfare.
The timing of his announcement caused surprise as hundreds of thousands of postal votes have already been distributed.
The Chancellor told BBC1's Andrew Marr Show: "The timetable for delivering that (the new powers) will be put into effect the moment there is a No vote in the referendum. The clock will be ticking for delivering those powers, and then Scotland will have the best of both worlds."
But Mr Salmond said: "This is a panicky measure made because the Yes side is winning. They're trying to bribe us, but it won't work as they have no credibility left."