THREE-FIFTHS of Scots believe Westminster would have to deliver "substantially more powers" to Holyrood than currently proposed if the SNP held the balance of power after May's General Election, according to a new poll.

The Panelbase survey found 60% of people thought the Nationalists could successfully use their clout in a hung parliament to extract more than the recent cross-party deal on tax and welfare thrashed out by the Smith Commission.

The poll, which was ­commissioned for the SNP, also found most people believed the greater the number of SNP MPs elected, the better Scotland's interests would be protected at Westminster.

The findings emerged just a day after an ICM poll for The Guardian suggested the SNP could cause a meltdown for Labour in Scotland next year.

It put support for the ­Nationalists at 43%, more than double the party's 20% vote share in 2010.

In contrast, support for Labour had nosedived from 42% to 26%, with the LibDems down from 19% to 6%, and the Tories slipping from 17% to 13%.

If those numbers were reflected in a uniform swing, Labour would go from 41 MPs in Scotland to just 10, severely reducing Ed Miliband's chance of replacing David Cameron as Prime Minister.

The SNP, meanwhile, would surge from six MPs to 45, ushering in a new era for Scottish politics.

The Panelbase poll found widespread agreement that greater devolution would flow from the SNP holding the balance of power at Westminster, with the majority of men and women holding the view.

Even 44% of No voters agreed compared to 32% who disagreed, with 51% of Labour voters and 44% of LibDem voters in 2011 also concurring.

Although 58% of men thought more SNP MPs meant better protection for Scottish interests, only 46% of women did, although support for the proposition was still ahead among both sexes, and in every age group and socio-economic class.

Among Labour voters in the 2011 election, 42% agreed compared to 37% who disagreed.

First Minister Nicola Sturgeon said: "As this momentous year draws to a close and we head into 2015 and the General Election, it is extremely encouraging to see more and more people put their trust in the SNP to stand up for Scotland.

"The fact that a substantial number of No voters and most people who voted Labour in 2011 agree that the more SNP MPs are elected, the better Scotland's interest will be protected, demonstrates the broad appeal of the SNP campaign.

"With a strong team of SNP MPs, we can ensure that Scotland's voice will be heard - using our influence to bring an end to austerity ­economics, make Scotland free of Trident nuclear weapons, and ensure that Scotland wins the necessary powers to build a fairer, more prosperous country."

The Smith Commission recommended giving Holyrood control of income tax bar setting allowances, more borrowing powers and control of some welfare benefits; it also said the Scottish Parliament should be made permanent, so that it could not be abolished without its own consent.

The cross-party Campaign for Scottish Home Rule is now consulting on how best to achieve the latter, and whether a written UK constitution is needed.

But the ICM poll of 1004 people found 30% thought the Smith recommendations did not go far enough, against 26% who said they were about right.

It found 53% thought Scotland should set its own corporation tax - an idea rejected by Smith.

Labour MSP Jenny Marra insisted Jim Murphy becoming Scottish leader marked a "fresh start".

She said: "We will come back in the new year with passion and energy, setting out our vision for making Scotland the fairest nation on earth.

"The choice facing Scots next May is clear - we can send SNP MPs to the House of Commons to protest against the Tories, or we can send Scottish Labour MPs to replace the Tories."

The Panelbase poll of 1018 adults in Scotland was conducted online between December 18 and 23.