The 'vow' did not sway the referendum result, new research shows

A survey of nearly 5,000 people, carried out on behalf of the research team by YouGov, found just 3.4 per cent of No voters said the so-called 'vow' was the main factor in their decision.

It emerged the principal reasons people voted No were because they felt British, they were concerned about unanswered questions and they believed independence would make Scotland worse off.

The study, Why Scots Voted No, is published today.

It offers the most detailed analysis to date of the referendum result.

The research reveals a huge gulf between Yes and No voters, with 41.3 per cent of independence supporters blaming the promise of more powers for their defeat.

Other independence supporters felt No voters had been influenced by media bias or had simply "lost their nerve".

The leaders of the three Better Together parties promised to fast-track "extensive new powers" for Holyrood on September 16, two days before the vote, when polls showed the Yes and No camps running neck and neck.

The plan had been devised and championed by former Prime Minister Gordon Brown.

Mr Salmond immediately identified it as the reason for his campaign's defeat. He said voters had been "misled" and "tricked" into backing No by a promise that amounted to "home rule" or "near-federalism".

The SNP has since criticised the programme of tax and welfare devolution that emerged from the Smith Commission as falling short of the vow and has put a demand for devo max at the heart of its election campaign.

Professor James Mitchell, of Edinburgh University, said: "When we look at the data we can see quite clearly that there is simply no great shift of people citing 'more powers' as a reason for voting No."

Dr Rob Johns, of the University of Essex, and another member of the research team, said support was shifting back to No before the vow.

He added: "It is not unusual for a misleading narrative to develop about what swung an election or referendum.

"According to our data, anyone who thinks 'it was the Vow wot won it' is exaggerating, to say the least.

"However, once these narratives develop, they can be hard to shift. And we may well see the effect of this one when voters turn out for the general election in May."

YouGov questioned 4849 people before and after the result.

Asked to give their main motivation, 29.5 per cent of No voters said they opposed independence felt British or believed in the Union.

A further 27.8 per cent said there were too many unanswered questions about the prospect of leaving the UK, while26.3 per cent said independence would leave Scotland worse off.

Some 5.3 per cent said they wanted to vote Yes but felt it was too risky and 5.2 per cent did not trust Mr Salmond. The remainder were unsure.

When independence supporters were asked what they believed motivated No voters, 41.3 per cent said they had been misled by the promise of further devolution.

A further 17 per cent claimed press or BBC bias influenced No voters.

Some 11.8 per cent said the 'electorate lost its nerve'; 11.2 per cent blamed warnings from the banks and business world, and 7.9 per cent said they had been swayed by Better Together's negative campaign.

Fewer than one per cent believed independence was rejected because Yes Scotland ran a bad campaign.

The rest gave other answers or were unsure.

SNP MSP Christian Allard said: "Undoubtedly, the Westminster parties published the Vow because all of their information indicated that it would have a big impact on the result."

But Scots Tory chief whip John Lamont, said the research showed people voted No "because they believe in the UK and didn't believe in Mr Salmond's flaky assertions".

And a Scottish Labour spokesman said: "While it is interesting to carry out these academic exercises, at the end of the day a substantial majority of the electorate voted to stay part of the UK."