By Paul Hutcheon
Scottish Political Editor

THE SNP government might not have the power to organise an independence referendum, according to one of David Cameron's closest allies in Scotland.

David Mundell, the shadow Scotland secretary, said there were "serious question marks" over the legality of calling such a poll.

And in a press briefing, Cameron twice dodged questions on the issue.

The development came as the Scottish Conservatives held their annual conference in Ayr at the weekend.

The Tories have been buoyed by the recent by-election victory in Crewe and polling which suggests Cameron will be the next prime minister.

SNP sources say the Nationalist government would be more likely to win an independence referendum in 2010 - their chosen date for the poll - if the Tories win the next Westminster general election.

The SNP intends to legislate for a referendum which would ask whether "the Scottish government should negotiate a settlement with the government of the United Kingdom so that Scotland becomes an independent state".

But Mundell, the MP for Dumfries-shire, Clydesdale and Tweeddale, said he was not convinced Holyrood has the power to organise a plebiscite. He said: "There are serious question marks about its legality, and there are also issues about the question and how the campaign would be financed."

But he said of the Calman Commission, which is reviewing devolution and Holyrood's powers: "If you have a proposal for major constitutional change it should be put to a referendum."

A source close to the First Minister said: "As has been clear all along, the question we will be putting forward is perfectly legitimate. David Mundell seems oblivious to this."

Asked at a briefing with journalists whether he accepted the legitimacy of Salmond's referendum proposal, Cameron dodged the question, saying: "We don't favour separation, we don't favour a referendum. We want to get on and govern the United Kingdom and succeed in the Scottish Parliament and deliver for people in Scotland."