Changes to the rules of succession to the throne are already under consideration. Ministers favour in principle the idea of allowing the heir to marry a Catholic, and see no clear reason why this should not apply to other faiths. Such moves could form part of the consultation process taking place over ending the bar on first-born females from succeeding to the throne.
David Starkey, a constitutional expert at the London School of Economics, said the bar on the monarch marrying a Catholic was set out in the Act of Settlement (1701), which did not refer to other faiths; but prospective royal spouses were required to be "in communication with the Church of England", or practising worshippers, which effectively extended the bar to other religions.
"Of course, it's outdated, but when you question it, you also question the role of the established Church and move towards the idea of a group of established religions. I think that is the way Prince Charles is going and I think that would be meaningless," Dr Starkey said.
Professor Eileen Barker, professor of sociology at the London School of Economics, said a royal marriage to a Muslim or Hindu would be welcomed by the majority of the ethnic group concerned. "The wife or husband would be a symbol for them. They would be delighted because it would mean that they would be recognised."
A spokesman for the London Central Mosque said: "If they are looking at the monarch to be, as Prince Charles suggested, a king of all faiths, then it will be sensible to reflect the make-up of Britain."
Yesterday it was revealed that the Way Ahead Group, the royal think-tank, has proposed limiting the title HRH to the inner Royal Family, and that bowing and curtseying should become "optional". Dr Starkey described this as a "sensible move". He said: "It addresses the question of hangers-on, but it does not mark a real shift."
A spokeswoman for Buckingham Palace indicated that there were no plans to strip the title HRH from existing holders, such as the Duchess of York's children, Princess Beatrice and Princess Eugenie, but the limitations were likely to apply to future generations.