Diana's brother, Earl Spencer, and her two sisters will hold their own private memorial service on the banks of the lake at Althorp, where Diana is buried. The Northamptonshire estate closes to visitors for the summer the previous day.

The earl remains unforgiven by the royal family, following his venomous address at Diana's Westminster Abbey funeral service. It was then that he pledged that his sister's "blood family" would look after Princes William and Harry, implying the Windsors were not up to it.

The princes turned down an opportunity to go on holiday this summer with Diana's sister, Lady Sarah McCorquodale, preferring tospend it with their father instead. The Prime Minister, Tony Blair, who strove to rescue the monarchy's reputation in the disastrous week following Diana's death, will also be at Balmoral.

Blair and his family have been invited to attend the morning service at Crathie Church on the day of the anniversary, Monday, August 31. The royals traditionally spend most of the summer at Balmoral, and the prime minister of the day is usually invited to spend the last weekend in August at the Queen's Scottish estate.

"The royal family and the Spencer family have obviously been in touch and each wishes to mark the anniversary privately and in their own way, wherever they may be on August 31," a Buckingham Palace spokeswoman said. "The royal family recognises that people may want to remember the princess in any number of different ways."