THE SNP could have a "paralysing effect" on the UK economy because of Nicola Sturgeon's refusal to rule out pushing for another referendum on Scottish independence, Nick Clegg has warned.

The Liberal Democrat leader insisted the First Minister was refusing to accept the result of last year's public vote in Scotland and was adopting a Maoist approach ie keep asking the people the same question until they come up with the answer you want.

Earlier this week, Ms Sturgeon failed to rule out putting a proposal for a second poll in the Nationalists' 2016 Holyrood manifesto, but said there would need to be a "material" change in public opinion or something else to do so.

SNP sources have made clear that the momentum for another referendum would have to come from Scottish voters; the party's hierarchy knows that if it were to propose a second poll, then it would have to be as near as certain of victory as another defeat could, as in Canada, kill off the independence cause for a generation.

In a key development, David Cameron signalled this week that a future Tory government would be minded not to allow a second referendum, stressing how the issue had been "settled" by the vote in September. Crucially, Westminster retains the constitutional power to sanction referendums anywhere in the UK.

On the campaign trail, Mr Clegg said despite the protestations of Ms Sturgeon and her colleagues that they had no plans to keep asking the independence question until they get the answer they wanted, " actually that is precisely what they intend to do".

He warned: "That would have a paralysing effect on the Scottish economy and would have a paralysing effect on the UK economy as a whole if we're constantly trying to guess every few years whether the SNP are going to get their way. They just don't seem to be able to accept the answer they received at the ballot box."

The Deputy Prime Minister went on: "There is almost a sort of Maoist tendency, which says that the people must be wrong according to the SNP and that they must be forced to ask themselves the question over and over and over again until they give the answer which is satisfactory to Alex Salmond and Nicola Sturgeon."

As some polls suggest the Lib Dems will lose all but one of their 11 seats in Scotland, Mr Clegg, asked if the Union was still in jeopardy despite the result of last year's referendum, replied: "Of course, there is a risk that the Union is pulled apart by a party, the SNP, whose sole purpose in life is to do just that.

SNP Westminster leader Angus Robertson branded Mr Clegg's claim 'silly.'