Cameron with Queen
Cameron will apologise to the Queen for impromptu remarksReuters

David Cameron is to apologise to the Queen for an "extraordinary breach of protocol" after he was caught on camera saying the Queen "purred down the line" with relief at the result of the Scottish referendum.

The Prime Minister's impromptu comments about the monarch's reaction to the result last week were picked up accidentally by a TV crew in Manhattan while he was talking with former New York mayor and media mogul Michael Bloomberg.

In the recording he said: "The definition of relief is being the prime minister of the United Kingdom and ringing the Queen and saying, 'It's alright, it's okay'. That was something. She purred down the line."

Audio experts at the BBC claim Cameron, who was in New York for the United Nations General Assembly meeting, then said: "I have never heard anyone tear up like that".

Royal protocol states politicians must not disclose any details of private conversations with Her Majesty.

Alex Salmond described Cameron's actions as "absolutely pathetic".

He told BBC Scotland: "David Cameron has been prime minister for four years and he hasn't learned basic civility on not gossiping about what Her Majesty The Queen thinks, or doesn't think, to Michael Bloomberg, or anyone else for that matter.

"That's absolutely pathetic and he should hang his head in shame."

Sources told the Daily Mail the Prime Minister will issue a private apology to Her Majesty over what experts described as an "extraordinary breach of protocol".

The Queen remained impartial during the Scottish referendum but the PM's comments suggest she was pleased with the majority vote of Scotland wanting to stay with the rest of the UK. Fifty five per cent of Scots voted against independence compared to 44% in favour of it.

Cameron also said he wanted to find the polling stations and "sue them for my stomach ulcers because of what they put me through. It was a very nervous moment."

A Downing Street spokesman confirmed he has since contacted Buckingham Palace and will apologise in person when he next meets the Queen.

When recently asked if he regretted the comments to Bloomberg.

He said: "Yes and yes. I'm very embarrassed about this, I'm extremely sorry about it. It was a private conversation, but clearly a private conversation I shouldn't have had and it won't happen again."