Scotland's referendum battle swung back towards the no camp on Wednesday night when an opinion poll gave the pro-union side a six-point lead, suggesting the sudden surge in backing for independence had subsided.
Hours after David Cameron, Ed Miliband and Nick Clegg travelled to Scotland to make heartfelt pleas to voters not to abandon the United Kingdom, the Survation/Daily Record poll put the no side on 53% against 47% for the yes camp once don't knows were excluded.
Immediately after the poll was announced the pound rallied on the foreign exchange markets, lifting over a cent and a half to $1.62 during the day, having slumped to a new 10-month low of $1.605, amid speculation that Survation might show the yes campaign ahead.
The poll – which gave the same margin as a Survation poll two months ago – came four days after the Better Together campaign was jolted by a YouGov/Sunday Times poll which placed the yes side in the lead for the first time – by 51% to 49% – in turn prompting Westminster's leading politicians to head north.
Alex Salmond, the Scottish first minister, said the latest poll showed that the yes side are the underdogs.
He told BBC1 Scotland: "I regard the yes campaign as the underdogs in this campaign. Why? Because we know that the Westminster establishment will throw everything – the kitchen sink and probably the living room – at the Scottish people over the next week."
Cameron had led the cross-party charge into Scotland with an outspoken plea to voters not to use the poll to give the "effing Tories" a kick as he said he would be heartbroken by a vote for independence.
In an appearance at the Edinburgh headquarters of Scottish Widows, where he appeared on the verge of tears, the prime minister said: "I care far more about my country than I do about my party. I care hugely about this extraordinary country, this United Kingdom that we have built together. I would be heartbroken if this family of nations we have put together – and we have done such amazing things – was torn apart."
The scale of concern at Westminster was highlighted as senior Tories said the prime minister would have to recall parliament in the event of a vote for independence to provide some stability amid fears that the pound would come under severe pressure.
"It would be inconceivable not to recall parliament in the event of a yes vote," said one member of the government, who predicted tough negotiations over the subsequent break up of the UK. "There would be utter convulsion of the British Isles," the Tory said. "There are horrendous, deep and difficult issues to be dealt with."
The atmosphere is likely to calm, for the moment at least, after the Survation poll. The pro-union camp will hope that warnings about the financial instability that would follow a yes vote may be cutting through.
Danny Alexander, the Liberal Democrat chief secretary to the Treasury, reinforced this point when he described the day as Salmond's "black Wednesday" after the Scottish financial industry giant Standard Life warned it would move pensions and investments out of Scotland to protect its UK customers after a yes vote.
Bob Dudley, the BP chief executive, urged Scotland to vote against independence next week, arguing that oil wealth would best be protected by remaining inside the UK.
Clegg visited the Scottish Borders to promise an "exciting chapter" of decentralisation not just for Scotland but England and the rest of the UK after a no vote.
"Whatever the result on the 18th – even if Scotland votes to remain part of the United Kingdom – the status quo is gone not only for Scotland but the whole of the United Kingdom," said the deputy prime minster as he appealed directly to Scots to vote no and stay in the UK.
He added: "We have done extraordinary things together – Team GB competed together, we defeated fascism together, we created the NHS."
The cross-party campaigning passed off without a hitch although Lord Prescott said in Rutherglen that Cameron was a hindrance to the no campaign.
The former deputy prime minister, who faced taunts from yes supporters, suggested Cameron was hoping for a yes vote to secure a parliamentary majority.
The new poll gave the no side a lead – by 53% to 47% – if the 10% of undecided voters are discounted. If the undecided voters are included, the survey of 1,000 voters found that 47.6% plan to vote no on 18 September, with 42.4% voting yes.
The Survation poll was carried out between last Friday and Tuesday this week – after YouGov first recorded a surge in support for the yes camp in a poll for the Times.
The Labour party, which was alarmed to see that more than a third of its voters plan to support independence, will be encouraged by the Survation findings which suggest that only a quarter of Labour voters, at 26%, were planning to vote yes next week. By comparison, 18.5% of SNP voters were expecting to vote no to independence.
Blair McDougall, the director of the Better Together campaign, said: "This fight for Scotland's future will go right down to the wire, but it's one we will win."
The response to the poll came after Miliband echoed Cameron's heartfelt plea for a no vote as he appeared in the once Labour heartland of Cumbernauld.
The Labour leader, who was careful not to appear alongside Cameron and Clegg to allow him to say that he is determined to unseat the Tories next year, said: "Friends, the only place to be today is in Scotland and not in prime minister's questions. I'm hear to listen, to talk and to make the case for Scotland staying in the UK."
The Labour leader indicated he would be staying in Scotland for most of the coming days, as both sides battle over the party's traditional working class vote.
Salmond mocked the appearance by the party leaders. He said: "Their concern – and this last gasp effort – seems to be with their own jobs. That is the contrast between the breadth and reach of Team Scotland and the narrow focus of Team Westminster."
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