SNP leader Nicola Sturgeon today left the door open to a second referendum on Scottish independence before 2020. Before last year's historic vote, Scottish nationalists insisted it was a once-in-a-generation chance to decided on the future of the 300-year-old Union. But Ms Sturgeon today refused to rule out demanding a re-run within the next five years, prompting opponents to claim she had 'broken a promise the size of Ben Nevis'. SNP leader Nicola Sturgeon today refused to rule out demanding a re-run within the next five years, prompting opponents to claim she had 'broken a promise the size of Ben Nevis' In September's vote, 55 per cent of Scots backed the idea of remaining in the United Kingdom. Alex Salmond said the vote was an 'opportunity of a lifetime' and two years ago, Miss Sturgeon said of the independence vote: 'We have always said it's a once in a generation thing.' But in a series of TV election debates between Scottish leaders, Ms Sturgeon has shifted her position and today left open the possibility that the promise of another vote could be included in a future SNP manifesto. Under pressure she said that 'something would have to change' before she promised a referendum, and people would have to vote for it. She said: 'I am not planning another referendum right now, there is not another referendum on the cards. 'In order for another referendum to be in an SNP manifesto in future, something significant would have to change from the situation we had last year in the referendum.' Ms Sturgeon, who was campaigning in Paisley today, left open the idea of demanding a referendum in next year's Scottish Parliament elections . Opponents claim Ms Sturgeon had 'broken a promise the size of Ben Nevis' on a referendum, after insisting last year's vote was a once in a generation event . During a fractious and at times shouty debate on BBC Sunday Politics Scotland, Scottish Tory leader Ruth Davidson challenged her to rule out another vote. Ms Davidson, leader of the Scottish Conservatives, added: 'You clearly don't want to tell people before they vote in this election, what will happen in the next election. 'You have a conference coming up in September, you have 80,000 new members who might be popping along, are you going to put a motion at your conference on this to put a referendum into your next manifesto?' Ms Sturgeon said: 'I am not planning another referendum right now, I haven't published the 2016 manifesto. It will be this time next year before we publish the 2016 one.' Mr Rennie said the SNP leader had 'broken a promise the size of Ben Nevis' on another referendum. He said: 'People need to know whether their vote for the SNP this time round will trigger a referendum in the SNP's manifesto in 2016. Nicola Sturgeon's refusal to answer this basic question makes clear that Scotland faces neverendum. 'It matters because during the referendum we know the SNP took their eye off the ball. As a result, public services were neglected. 'We have seen from Canada the economic impact of an uncertain constitutional environment. Quebec lost jobs and wealth. That damaged the province in the long term. I want a Scotland which builds a stronger economy and a fairer society, balancing the books and delivering more powers.' During a TV debate, Scottish Labour leader Jim Murphy and Tory leader Ruth Davidson challenged Ms Sturgeon to come clean on her plans for Scotland . Ms Sturgeon later accused her opponents of 'reviving Project Fear'. The First Minister was questioned about SNP plans to increase Scotland's financial powers, which economists have suggested would leave a £7.6 billion spending gap, during a third televised election debate in under a week. Ms Sturgeon said that full fiscal autonomy would take several years to implement but with new powers Scotland would start growing its economy and revenues. She said: 'This week we've seen the Project Fear that dominated the referendum revived by these three unionist parties, trying to talk down Scotland and assert that we're not capable of running our own affairs.' Scottish Conservatives leader Ruth Davidson said: 'This (the figure) didn't come from us. You're right in saying this came from the Institute for Fiscal Studies. It also came from a group of Scottish-based economists that projected the gap to be bigger.' Scottish Labour leader Jim Murphy said: 'To make this £7.6 billion up Scotland would have to grow at twice the rate of the rest of entire advanced world, so how would you do that Nicola?'
SNP leader refuses to rule out calling for another vote on independence . Nationalists had called last year's referendum 'once in a generation' Opponents accuse Sturgeon of breaking a 'promise the size of Ben Nevis'