Highgrove House: party venue

Charles Splashes Out on Camilla

He had a marquee set up in the garden of the Georgian house so 80 guests could celebrate the occasion with a five-course dinner under cover.

Mrs Parker Bowles - whose actual birthday was on Thursday - was the first to arrive, smiling broadly for the numerous photographers crowded outside the gate.

The party, thought to have cost the prince about £30,000, came at a time of renewed speculation about their relationship and possible marriage plans.

Camilla Parker Bowles (left) arriving with her sister

On Thursday, the prince's local vicar said Charles should not become head of the Church of England - as King - unless he repented of his adultery and gave up Mrs Parker Bowles.

It was the first time that the Reverend John Hawthorne, the vicar of Tetbury in Gloucestershire, had spoken about the relationship.

"I do not see how he could be Defender of the Faith of a church whose laws, whose rules and teachings he is ignoring, being an admitted adulterer, perhaps unrepentant - and certainly if he married Mrs Parker Bowles he would be an unrepentant adulterer," said Mr Hawthorne.

Rev John Hawthorne: Church should have a say

He also said that the church would have to decide how to deal with the relationship rather than ignoring it. "The church has got to have a role and has got to state its mind," he said.

On Thursday, the Prime Minister was briefed about the legal and constitutional implications of the divorced prince marrying a divorcee and then ascending to the throne. Some MPs have expressed concern about the repercussions on the Church.

The Labour MP Tony Wright, who chaired the cross-party group on the constitution in the last Parliament, insisted the issue had to be resolved.

"Eventually, crisis will produce a change and unfortunately it seems that it is out of crisis that it's going to happen again," he told BBC Radio 4's Today programme.

He suggested that one option was for the Church of England to "live with" the Prince's lifestyle, as the nation would rather have a happy monarch.

"Either you have a Supreme Governor who can manage his life in the way other people manage it and when they encounter difficulties have to solve them, or be told by this established Church that they can't do it," said Mr Wright. "In which case we shall have a constitutional crisis and it will end in dis-establishment."

The main legal obstacle to the marriage remains in the hands of the Queen. Under the Royal Marriages Act of 1772 the monarch can veto any marriage of a descendent of King George II.

If Charles were to marry Mrs Parker Bowles and then ascend to the throne she would become the Princess of Wales, in the first instance and then Queen Consort.

The attitude of the Palace is, at present, against the couple marrying.