Support for Scottish independence has risen by eight points in the last month, in a poll described as a "breakthrough" by yes campaigners.
The YouGov poll released on Monday night put the lead for the no campaign at six points, down from 14 points in the middle of August and 22 points early last month.
The poll for the Sun found that 48% of voters said they would vote no to independence, with 42% planning to vote yes and 8% saying they did not know or would not vote. Excluding "don't knows", 53% of those polled planned to vote no, while 47% would say yes.
This is a huge boost for the morale of the yes campaign, particularly because YouGov has regularly reported lower levels of support for independence than other polling companies.
Writing in the Sun on Tuesday, the YouGov president, Peter Kellner, described the independence campaign as being "in touching distance of victory".
The results come after a strong performance by the Scottish National party leader, Alex Salmond, in the second televised debate against Alastair Darling, and as the yes campaign continues to hammer home the message that a yes vote is the only way to protect the NHS from Westminster's privatisation agenda.
Blair Jenkins, the head of Yes Scotland, said: "This breakthrough poll shows that yes has the big momentum. We only need another three-point swing to achieve a yes for Scotland on 18 September.
"While the no campaign press the panic button and blame each other for a series of blunders, yes will get on with the job of persuading more of our fellow citizens – both no and undecided voters – that we need a yes vote to put Scotland's future in Scotland's hands."
The pro-union Better Together campaign last week faced criticism after it launched an advert aimed at undecided female voters that was derided as "patronising" and "sexist".
The Better Together campaign director, Blair McDougall, said: "We need the silent majority who back a no vote to do their bit. Whether it's voting on the day, knocking on doors, making phone calls or speaking to friends and family, the silent majority should feel confident in speaking up.
"The nationalists talk as if they are winning but the truth is, this is yet another poll showing the campaign for Scotland to stay in the UK in the lead."
Analysing the poll on Tuesday, John Curtice, professor of politics at Strathclyde University, said the yes campaign had "made particular progress amongst the less well-off C2DE social groups, at whom much of its campaigning has been targeted in recent weeks". Support for independence among those voters was up nine points from last month, while wealthier ABC1 voters showed a more modest swing of six points.
"Doubtless this helps explains why support for yes amongst those who voted Labour in 2011 has increased over the same period from 18% to 30%," Curtice wrote on the website What Scotland Thinks.
He noted that older voters were still resisting the pull to yes, despite the importance of the NHS for this demographic, and asked "will pensions now be one of the crucial battlegrounds in what promises to be a very keenly contested last two weeks?"
Voters in Scotland have until midnight on Tuesday to register for the referendum. Local registration centres say they have received tens of thousands of applications in recent days. A high turnout is expected on polling day, with many predicting that it will be higher than 80%.
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