OPPOSITION to independence is surging, with supporters of the Union opening up a 25-point lead over the Yes campaign.

A new poll published today reveals 53% would vote No to independence, compared to 28% who are in favour of breaking up the United Kingdom.

A little over a year ago support for independence had edged ahead in the battle for Scotland's future, but since then there has been a significant change in public opinion, which would appear to have been enhanced by a summer of unprecedented British sporting success.

The latest survey by pollsters TNS-BMRB comes as The Herald can reveal a deal has been done on the vote, with the historic signing of an agreement between Prime Minister David Cameron and First Minister Alex Salmond to take place next Monday in Edinburgh. The final details of the referendum will be announced next week following talks this week between Michael Moore, the Scottish Secretary, and Nicola Sturgeon, the Deputy First Minister.

A source stressed the SNP Government has not been forced into agreeing anything and has been fully supportive of the process and the agreement reached.

"Everything has fallen into place," said the source, who has full knowledge of the inter-governmental talks.

The Herald understands the long-awaited publication of the results of Holyrood's consultation process will "match" the agreement reached by London and Edinburgh – and come out against having a second question on the ballot paper.

One key development is that 16 and 17-year-olds will be given the vote for the first time in a poll in the UK.

So far this year the pollsters have carried out three surveys with the numbers opposing independence rising from 44% to 50% and now 53%. At the same time the Yes camp has declined from 38% last year to 35%, 30% and now 28%.

The number of undecided respondents has fluctuated over recent years to reach 25%, but it has fallen in each of this year's three polls and is now 19%. Even if the pro-independence campaign could persuade every doubter to come across to its camp, it still would come nowhere near bridging the present 25-point gap.

A sample of 995 adults was interviewed in their homes across 70 con-stituencies between September 26 and October 4, a period that began the day after Labour leader Johann Lamont's dramatic policy reversal in coming out against universal benefits.

Chris Eynon, head of TNS-BMRB Scotland, said: "With the referendum not due for two years, much can change. However, there is no doubt that momentum currently sits with those opposed to independence.

"This may be on account of a feel-good factor from British sporting achievement over the summer, the fact that every week seems to bring a fresh challenge to the viability and status of an independent Scotland or simply the SNP Government becoming increasingly challenged on its performance.

"The Yes campaign is very much on the back foot and struggling to get its message across."

In October 2011 the polling firm began asking an additional question testing voters' views on whether Holyrood should be given greater powers short of independence.

That first poll showed a relatively even three-way split, with 33% for more powers, 29% for the status quo and 28% for independence. After some fluctuations, the latest poll puts the status quo top, with 35%, one point ahead of those seeking more powers, with independence languishing at 22%. Mr Eynon said: "The appetite for constitutional change among some within the Scottish electorate seems to be waning and it remains to be seen if this continues as the referendum draws near."

Voters in Glasgow in particular appear to have turned against independence, with 21% saying they would vote Yes, the lowest of any part of Scotland, and 65% voting No, the highest. Among males across the country, 32% would vote Yes, 51% would vote No, with 17% undecided.

For women the figures are 24% for Yes, 56% for No, and 21% undecided. Support for independence is highest among those aged 18-24 (37%) followed by those aged 45-54 (32%).

The No vote support reaches 65% among those aged over 65.