Wyre Davies in Newport: "A technically illegal joint of beef"

The prince ate the meat during a visit to Wales on St David's Day - as did Welsh Secretary Alun Michael, whose colleague Nick Brown, the Agriculture Minister, extended the ban only last month.

Prince Charles, according to sources, knew that the beef had been on the bone and was happy to eat it. This contrasts with comments from a Welsh Office spokesman who said Mr Michael had been unaware it had been on the bone.

The joint at the centre of the controversy

The prime minister's spokesman said of Mr Michael: "Had he known it was taken from a cut that would be banned for sale he clearly would not have done it."

A spokeswoman for Newport County Borough Council said its environmental health department would be "investigating" the incident.

The Celtic Manor Hotel issued a statement apologising to the Prince and Mr Michael.

"We have received conflicting advice on this (the ban) from various sources and feel there is a need for the regulations to be clarified.

"In the meantime, we would like to extend our sincere apologies to His Royal Highness, the Secretary of State and Welsh Beef Promotions for any problems this may have caused them."

The BBC's environment correspondent Richard Wilson says Prince Charles was offered and accepted a slice of meat carved from the bone right in front of him.

He ate it before launching a campaign promoting Welsh beef and lamb in Newport, south Wales, then said: "I am only sorry that so many of you have had to wait in here building up an enormous appetite whilst having to look at this huge hunk of roast beef.

The BBC's Richard Wilson: "He has cocked a snook"

"I am sorry that I got there before you did. Shortly, you will be able to taste it like I did. It's absolutely delicious."

Chairman of the Welsh Lamb and Beef Promotions, Rhys Roberts, insisted no offence had been committed.

"It was not for sale, there was nothing illegal about it. Prince Charles saw it and it was part of his walk through the various samples that he was looking at. It was there for everybody to see," he said.

Mr Roberts' colleague Lynda James added: "It's only against the law if we sell it to the customer. The hotel did not sell it to us and we did not sell it to the prince."

This was not the first time the prince has eaten beef on the bone since the ban came into effect in 1997.

He was sent a rib of beef by Welsh farmers last year and returned a note to them saying it was delicious.

By so openly eating beef on the bone, our correspondent says Prince Charles has effectively "cocked a snook" at the government.

The ban was introduced in 1997 after scientific evidence showed there was a risk of people contracting Creutzfeldt Jakob Disease (CJD), the human form of "mad cow disease".

There were hopes that it would be removed in February but the government accepted medical advice and extended the ban for another six months.