London - Queen Elizabeth II's eldest grandchild could lose his place in the line of succession to the British throne if he marries his Catholic fiancee, newspapers reported Friday.

Prince William, Prince Harry, Peter Phillips and Zara Phillips are seen here in 2005. Queen Elizabeth II's eldest grandchild, Peter Phillips, could lose his place in the line of succession to the British throne if he marries his Catholic fiancee, newspapers have reported. [Agencies]

Citing sleuthing work by Catholic weekly The Tablet, newspapers said Peter Phillips' Canadian fiancee Autumn Kelly, 31, was baptised as a Catholic in Quebec.

The 1701 Act of Settlement bars monarchs or their heirs from becoming or marrying Catholics.

Phillips, 29, is the only son of the monarch's daughter Princess Anne and her first husband Mark Phillips. He was Queen Elizabeth's first grandchild and is 10th in line to the throne.

He met Kelly, a management consultant, at the Canadian Grand Prix in Montreal in 2003. The engagement was announced last Saturday.

Kelly was baptised in 1978 at St John Fisher parish church in Pointe-Claire, a Montreal suburb.

A spokesman for the church told The Daily Telegraph newspaper that Kelly's mother Kitty had authorised the information to be disclosed, saying her daughter was proud of her religion.

Buckingham Palace, the queen's official residence, told the newspaper that a wedding date had not been set and "if a decision has to be made, it will be made at the time of the marriage."

The fact that Catholics are barred from the line of succession angers many within the church. The monarch is the head of the Church of England, but there is no restriction against the sovereign marrying a member of a faith other than Roman Catholicism.

The Guardian newspaper's People column speculated that the law would be swiftly changed if Prince William, second in line to the throne, seemed set to marry a Catholic.

Prince Michael of Kent, a cousin of Queen Elizabeth and a grandson of king George V, lost his place at 15th in the line of succession when he married Baroness Marie-Christine von Reibnitz, a Roman Catholic, in 1978.

Phillips's younger sister Zara is an accomplished horsewoman and is currently the World and European eventing champion. He has earned a cap for the Scottish Schools rugby union team.

After graduating in sports science from the University of Exeter, south-west England, Phillips worked for the Jaguar and Williams Formula One racing teams and currently works at the Royal Bank of Scotland in Edinburgh.

Like his sister he does not have a royal title and does not carry out any official engagements. He generally keeps a low public profile, although he is often seen at important national events.