Labour's shadow chancellor has urged undecided voters in Scotland to "think hard" about how they will cast their ballot, as he warned a vote for the SNP would put the country on the road to a second independence referendum.

Ed Balls travelled to Glasgow where he made a last-ditch plea to those who have not yet made up their minds.

With a poll showing almost 30% of voters in Scotland are undecided, he said: "I'm saying to all those undecided voters, think hard about this, because it is so important what you are going to do. A vote for the SNP is a vote for plans which extend austerity and let the Tories back in."

In a speech to party activists he insisted the "SNP's priority has never been about ending austerity", claiming nationalist proposals for full fiscal autonomy would result in a £9.7 billion gap in Scotland's public finances.

Mr Balls said: "The SNP cannot hide from the facts any longer. The SNP plans would mean longer austerity, bigger cuts, more debt and less money for public services than Labour's plans. It is not fiscal autonomy but extended fiscal austerity if the SNP get their way in the next parliament."

But he added: "The SNP's priority has never been about ending austerity. SNP MPs aren't trying to go to Westminster to fight poverty, they want to go to Westminster to fight for another referendum.

"That is why we do face two roads and we're going to decide in the next 10 days which road to take - Labour's road, a better plan, a road to an economy which works for working people, or a road to another referendum. That's the choice."

He was speaking as a new poll by TNS put support for Nicola Sturgeon's SNP at a record 54%, up two percentage points from the previous poll, compared with 22% for Labour.

But the same poll also found 29% of those who said they are certain to vote are still to make their minds up - a larger proportion of undecided voters than there were at the same stage in the referendum campaign.

While polls across the UK point to another hung parliament being the most likely outcome of the May 7 election, Labour has ruled out doing any deals with the Scottish nationalists.

Mr Balls said: "The reason we've said consistently no coalition with the SNP, no deals, is because the SNP not only do they not support what's in our manifesto, they want something fundamentally different from what's in our manifesto.

"We want to show we can all work together and we can have a stronger and fairer future together, and the SNP don't want that.

"That is why we have said consistently we're not getting into any talk about pacts, agreements, confidence and supply. Nothing has changed, we've insisted on that all the way."

Scottish Labour leader Jim Murphy, who joined Mr Balls in Glasgow, said the SNP "plan to use this General Election to stoke up discontent and division so they can push for a second referendum".

He added: "It is the nationalists' clear intention to pursue a second referendum sooner rather than later if they are given the opportunity.

"They would consign Scotland to years of deepening division while the needs and priorities of working-class Scots are set aside for another day, another year or indeed another generation.

"SNP MPs will be working every day for another referendum, rather than working hard for working Scots. That's the choice we now face in just 10 days. A party that exists to build a fairer economy, or a party that exists to hold another referendum.

"We can take that road in 10 days to a fairer Scotland or we can take a different road, a road to a second referendum."

Mr Murphy said: "There's a third of voters who are undecided, the number in Glasgow is even larger. This is the election in our lifetime with the largest number of undecided voters this close to a General Election."

But he warned that if the current opinion polls are replicated on election day, it would "turbo-charge the SNP's campaign for a second referendum".

Former Liberal Democrat leader Charles Kennedy accused the nationalists of having "gone back" on their commitment that last year's independence referendum would be a once-in-a-generation event.

However he also accused the Tories of "sowing division" across the UK by "stoking up English nationalism".

Mr Kennedy said: "The Liberal Democrats will not put our unity at risk, so in each of the 11 Scottish Liberal Democrat seats it is a straight choice.

"It is a choice between the Liberal Democrats, who will grow the economy and invest in the NHS, or the SNP who want a second referendum and ramp up the debt."

He insisted: "The Liberal Democrats are best placed to stop the SNP. Any other vote will let the SNP in across Scotland and put the economic recovery and unity at risk."