Alex Salmond insisted David Cameron's pledge of a poll by November 2017 had also "completely changed" the nature of the independence debate, with the SNP leadership saying it meant the best guarantee of Scotland staying in the European Union was a Yes vote in next year's referendum.
The Prime Minister, in his long-awaited landmark speech on Europe delivered in the City of London, said with "courage and conviction" a future Tory government could renegotiate Britain's membership of the EU, bringing back powers to Westminster.
An in-out referendum, where the public would have the final say, would be held by November 2017 and he would campaign "heart and soul" for it.
However, when asked if he would lead a campaign to get Britain out of the EU if he failed to get a renegotiated settlement, Mr Cameron side-stepped the question, insisting he did not enter negotiations "expecting to fail" and that while talks would be tough, there was "every chance of success".
Later, during a rowdy Prime Minister's Questions, the Labour leader claimed Mr Cameron had been driven to offering an in-out referendum "not by national interest but dragged to it by his party". He repeatedly asked Mr Cameron what he would do if he did not succeed in getting a renegotiated settlement, but the Prime Minister goaded Mr Miliband into ruling out an in-out referendum.
The Labour leader told MPs: "My position is no, we don't want an in-out referendum," adding: "Six months planning a speech on a referendum, he can't even tell us if he's for yes or for no."
Grant Shapps, the Conservative Party chairman, claimed Mr Miliband had been bounced into ruling out an in-out referendum, saying: "It's clear that Labour doesn't trust the British public to have their say on their country's future."
Senior Tory sources told The Herald they believed Mr Miliband had made a strategic error. One was asked if the Conservatives believed the promise of an in-out poll was a vote winner. She replied: "Yes, absolutely. It's always in the national interest for people to have their say."
Later, Douglas Alexander, the Shadow Foreign Secretary, sought to clarify Labour's position. He made clear it was against an in-out referendum for now because it would be bad for jobs and stability.
Asked if it could be in favour in the future, he replied: "That's not a decision we could or should sensibly make now."
While Mr Cameron's poll pledge won strong backing from his Eurosceptic Tory colleagues – London mayor Boris Johnson said it was "bang on" – it exposed the rift within the Coalition.
Nick Clegg, Deputy Prime Minister, insisted the priority was jobs and growth, and a referendum would mean "years and years of uncertainty because of an ill-defined and protracted renegotiation of Britain's status within the European Union".
At Holyrood, the First Minister said the PM's speech was "fundamentally confused".
"On the one hand he is trying to appease the Eurosceptics on his own backbenches and on the other he is trying to appear as a European reformer. He is trying to ride two horses at the same time and it is inevitable he will fall off before long."
Mr Salmond said the promise of an in-out poll changed the debate in Scotland.
"The Westminster parties have consistently claimed a referendum on Scotland's independence causes uncertainty. It is now clear the persistent undercurrent of Tory Euroscepticism poses the biggest threat to Scotland's position in the EU and has now helped to hole below the waterline the baseless scaremongering of Alistair Darling and the rest of the No campaign."
Scottish Labour leader Johann Lamont said the Conservatives and the SNP shared the "same destructive agenda". She said: "Yes, people want reform to the UK but the overwhelming majority of Scots and the people of Britain want Scotland to remain in the UK. And while we all want reform to the European Union, the majority of people want to remain in it."
She said Mr Cameron and Mr Salmond were "putting their own party interests ahead of the interests of the people they should be serving".