A REFUSAL by Whitehall to hold a referendum on Scottish independence would have been "disastrous" for the United Kingdom, David Cameron has insisted, saying that politicians had to trust the people.

And the Prime Minister declined to answer whether he had nightmares about the prospect of a Yes vote in September, refusing also to reveal what he would say to the Queen if Scotland voted to leave the Union.

Mr Cameron, who visited Scotland last week to promise more powers for Holyrood and is intent on several more visits before Referendum Day, stressed that when faced with a choice, the right thing to do was to sanction the independence poll.

"You can't hold people in an organisation against their will," he declared. "Perhaps the best slogan that Conservatives ever had was 'trust the people' and that's what I am doing."

Acknowledging the SNP's landslide victory in 2011 at the Scottish parliamentary elections, he explained: "If I had said as Prime Minister: no, you can't have it; and if we'd have had a two-year- long battle about whether or not Scotland had the right to choose its future, that would have been disastrous for the United Kingdom."

The PM noted how "trust the people" was a deeply Conservative view of life; that, in the end, "you should trust people rather than bureaucracies and institutions to chart the right course".

Asked about whether he had considered delaying it, Mr Cameron replied: "Postponing it would have been the same thing. The Scottish people would have felt: hold on, this should be our decision. Giving them a referendum, which is decisive, legal, fair, irreversible and binding, that is the right thing to do."

Asked what he would say to the Queen after a Yes vote, when she might angrily suggest he had betrayed Britain, Mr Cameron replied: "These conversations are strictly private and I sometimes reflect, as one of my predecessors did, that it's probably the only private meeting you have all week."

Tomorrow night in Glasgow, Alistair Carmichael in a speech at the Scottish Engineering annual dinner will make clear a No vote is a "positive vote" for change that will produce more powers for Holyrood.