In his book The Monarchy and Constitution he says that the wife of the king automatically becomes queen. "A divorce between the Prince and Princess of Wales would prevent the Princess of Wales becoming queen, since she would no longer to be the wife of the king." But as mother of the future monarch, she expects a role and a title to be found for her.
The present arguments are what these should be - with the Princess reputedly demanding more than her estranged husband is willing to offer.
Buckingham Palace refused to discuss the possibilities yesterday, but the Royal Family has wide powers over titles. Some sources suggested she would be likely to lose the honour of Her Royal Highness. But Dr Rodney Barker, of the London School of Economics, said: "One can speculate that the Palace could allow the use of the title Princess Diana."
The new job is proving as difficult as the title. In the weeks since her Panorama interview, the Princess has had talks with the Palace and the Prime Minister about her desire to be a roving ambassador for Britain.
On Wednesday, just hours before the Queen's letters became public, John Major had a further meeting with the Princess at her home in Kensington Palace.
Some members of the Government have expressed disquiet at the prospect of a loose cannon of a disaffected princess touring the world. Yet divorce could help resolve the fears by clarifying her position and laying down ground rules.
Independence would also have the benefit of easing the pressure on her personal life. In recent months, she has complained to friends that it is impossible for her to enjoy amicable relations with any man without him coming under public scrutiny.
A life in a new residence away from the stuffy confines of Kensington Palace would give her a freedom which has been impossible within the Royal Family.
Both sides deny there have been any talks between Prince Charles's lawyers at the "royal" firm Farrer & Co, and the Labour peer Lord Mishcon, acting for the Princess.
But legal experts believe that she could be in line for a pounds 15m, "clean- break" settlement which would provide her with a net annual income of pounds 500,000.Reuse content