Survey finds support for independence jumped six points in the last month, putting yes vote at 38% and no vote at 39%

A dramatic surge in support for Scottish independence has been confirmed by a further poll that shows that next week's referendum is on a knife edge, with a gap of just one percentage point between yes and no.

The poll by TNS found that support for independence has jumped by six points in the last month, putting the yes vote at 38% and the no vote at 39%, wiping out a 12-point lead for the pro-UK campaign led by former chancellor Alistair Darling.

The switch in support will delight the yes campaign but deeply alarm their opponents, coming after a YouGov poll found the pro-independence vote had a narrow one-point lead for the first time.

With only 10 days until the referendum, news of the YouGov poll led to several billion pounds being wiped off the value of leading Scottish companies on Monday and a further drop in the value of the pound.

The stock market value for Edinburgh-based Lloyds Banking Group fell by 3.3% or £1.7bn by Monday lunchtime, with RBS shares falling 2.8% or £1.1bn, and energy company SSE's shares dropping 2.7% or £400m.

TNS had originally planned to release its findings overnight on Tuesday, but brought that forward after worried City analysts and market traders called them about their poll, for the first time, following YouGov's findings.

Another poll released on Sunday by Panelbase for the pro-independence campaign Yes Scotland found the no vote was still in the lead, at 52% compared with 48% for yes, excluding the undecided.

Yes Scotland responded cautiously, saying: "Yes has the big momentum – with support growing particularly strongly among Labour voters and women – but we still have work to do if we are to win."

Denis Canavan, the chairman of Yes Scotland's advisory board and former Labour MP, told a rally in his hometown of Cowdenbeath: "We are now on the very cusp of making history – a bold and confident new Scotland, run by the people of Scotland and built on enduring principles of equality, fairness and social justice.

"This new Scotland could be less than a fortnight away. But we must not be complacent. The scaremongering, dissembling and misrepresentation of the no campaign will be ramped up as we approach polling day."

Their rivals at Better Together said the latest findings contradicted their own polling and tens of thousands of voter contacts, and insisted they would not change direction: "We're genuinely baffled because it's just not what we're getting back, so our message is still the same."

He said their polling did not show the race was neck and neck. "I honestly have zero evidence that that is the case. We honestly just don't understand this poll. All the numbers coming in from every part of the country from huge amounts of contacts every day tell us something different. "

TNS, which interviewed 990 people face to face, found the number of undecided voters had increased to 23%, implying that up to 600,000 voters still had to make up their mind.

It said among those certain to vote, no and yes were tied on 41%, but the long-term trend for TNS implied that undecided voters were moving to yes. In another finding, its sample felt no would still win, by 45% to 31% predicting a yes victory on 18 September. Only 56% of yes voters were confident they would win.

TNS said the only age group where the no vote was in the lead was the over-55s – mirroring YouGov's findings on Sunday. Among all voters aged under 55, there was a nine-point majority for yes.

TNS added there had been a strong move to yes among women, with the number planning to vote yes rising from 27% a month ago to 35% this month.

Tom Costley, head of TNS Scotland, said: "This poll reveals a remarkable shift in voting intentions, but the signs were evident in our last couple of polls which indicated a narrowing of the no lead, especially amongst those who told us that they were certain to vote.

"It is too close to call and both sides will now be energised to make the most of the last few days of the campaign and try and persuade the undecided voters of the merits of their respective campaigns."