Camilla Parker Bowles will automatically become Queen when the Prince of Wales succeeds to the throne unless there is a change in the law, the Government confirmed tonight.
The Department for Constitutional Affairs admitted legislation would be needed no matter what Camilla wished to call herself when Charles becomes King, to prevent this happening.
It is believed to be the first time that the Government has acknowledged this stance on the record.
Clarence House has previously insisted that the Government agreed with its view, taken from legal advice, that it was only a convention for the wife of the King to be known as Queen.
The Prince's aides did admit, when the royal engagement was announced, that legislation might be needed to tidy the issue up later on.
Mrs Parker Bowles will be known as the Duchess of Cornwall after her marriage at Windsor on April 8 and intends to take the title Princess Consort when the Prince accedes the throne.
A Department for Constitutional Affairs spokeswoman confirmed that legislation would be needed for Camilla not to become Queen automatically on Charles's succession.
"I think traditionally that's probably the case because in all similar circumstances in the past in past royal marriages that is what has happened," said the spokeswoman.
"But I think she is not going to be referred to as Queen, she will be referred to as the Princess Consort." Asked about the position of other countries where the Prince of Wales would become head of state on his succession, the spokeswoman replied: "I think you are right in thinking it would require legislation for her not to be Queen."
Tony Blair's official spokesman said: "The position at the moment is limited to what the title would be on her marriage. In terms of any future events, let's wait until future events arise."
On the question of whether Mrs Parker Bowles would automatically become Queen in the absence of legislation, the spokesman added: "I'm not disputing what you have said."
A Clarence House spokesman said tonight: "With any legal situation there are always different views.
"If the Government said legislation would be needed it wouldn't be a problem. It can easily be done in the Civil List Act. "This is something which is a long way in the future, we hope."
Earlier the Government confirmed that the marriage will not be "morganatic", which means that the couple's decision not to call her Queen Camilla will have no legal standing.