DAVID Cameron has admitted he would have wanted to stand down if there had been a Yes vote, but says he would have soldiered on out of a sense of duty.

Ahead of the Scottish referendum many argued that losing the Union would have made his position untenable.

When the matter of his resignation was raised, the Prime Minister repeatedly said the issue did not arise and the referendum was not about his future but that of Scotland and the UK.

But asked in a newspaper interview yesterday about the possibility of him standing down if Scots had voted for independence, he admitted: "I thought about it a lot. Emotionally I would have been very winded and wounded. I thought in many ways that is what I would want to do."

Mr Cameron even contemplated the speech he would have had to have made from the steps of No 10 in the event of a Yes vote.

He said: "Obviously, I thought what I would have to say if there was a Yes vote. I would have felt it as a huge blow. I'm very glad I didn't have to say it."

But the PM stressed that on reflection he would have wanted to remain in post even if the result had gone the other way.

"I just don't think [resigning would have been] the right thing to do. The job of the United Kingdom Prime Minister, whatever the outcome, would be to knuckle down and get on with the job.

"It would not have been doing your duty."

The PM, who had previously revealed he had only seen highlights of one of the Salmond versus Darling TV debates, said he stayed up all night to watch the referendum results.

"I did not sleep," he declared. "I went to bed and tried to sleep but I came down to the press office about three o'clock as the results came in. My children got up: they sensed how worried I was by it. They sat on my knee as the results came in."

Mr Cameron yesterday also pledged "never again" to discuss his conversations with the Queen.

He was challenged on the BBC's Andrew Marr Show about whether he was ashamed to have been overheard saying she had "purred" when told the result of the Scottish independence referendum.

He said he regretted the exchange between himself and former New York mayor Michael Bloomberg, which was picked up by TV microphones at the United Nations last week.

Mr Cameron said: "(It is) one of those moments when you look back and kick yourself very hard. It was not a conversation I should have had, I am extremely sorry and very embarrassed about it.

"I have made my apologies and I think I'll probably be making some more."

Asked if he felt ashamed, the Prime Minister added: "I'm very sorry about it … I'm not going to ever discuss my conversations with the Palace ever again."

Downing Street has already contacted Buckingham Palace to offer the Prime Minister's apologies.

Mr Cameron will say sorry in person when he next meets Her Majesty at Buckingham Palace after her return from Balmoral.

Microphones caught Mr Cameron telling Mr Bloomberg: "The definition of relief, if you are Prime Minister of the United Kingdom, is ringing up Her Majesty the Queen and saying 'Your Majesty, it is all right, it's okay'," Mr Cameron said.

"That was something. She purred down the line."