Ministers are hushing up an opinion poll paid for with £50,000 of taxpayers' money that shows a surge in support for Scottish independence, an MP has claimed.

The Scottish National Party's Angus MacNeil (Western Isles) called on the Government to be straight with the public and publish the report.

It is said to have been conducted by Ipsos Mori, and its existence was revealed by Kelly Brown, who sent a letter to a newspaper claiming she worked for the firm and saying the results had not been published because they showed a surge in support for independence.

In the letter, she wrote: "A recent poll commissioned by the Cabinet office was 'buried' as it returned a result which showed the Yes vote was soaring."

Ipsos Mori have declined to comment, other than to tweet that it employs no one by the name of Kelly Brown.

During Deputy Prime Minister's questions in the Commons, Mr MacNeil asked Nick Clegg: "Your Government has actually hushed up an opinion poll from the taxpayers who paid for it at a cost of £50,000.

"The poll reportedly shows a surge in support for Scottish independence.

"Tory and Labour scare stories are not working. There should be no government secrecy. So will you be straight with the public on independence and publish this poll? There's not reason that this should be kept secret."

Mr Clegg replied: "I've learnt to try and be a bit wary about opinion polls.

"The only poll that counts is the poll that's going to happen on September 18 and I very much hope, and I think people even like myself who don't have a vote, those of us south of the border, fervently hope the Scottish people will decide to remain part of the family of nations that makes up the United Kingdom.

"Because there is so much that we can do together that we simply cannot do apart and that's very much the argument that I hope will prevail on September 18."