Her sons, Princes William and Harry, will attend a family prayer service at Crathie Church, Balmoral, with the Queen, the Prince of Wales and Prince Philip.

Althorp, where the princess is buried

The princess's brother and sisters will hold a private memorial service on the banks of the lake at Althorp, by the island where she is buried.

It was at Balmoral that the Royal Family first heard of the tragic Paris crash and Diana's death early in the morning of August 31 last year.

And it was to Crathie Church that the young princes were taken as they were coming to terms with the shock at the news.

This time the royals will be joined by Prime Minister Tony Blair and his wife, Cherie, who will be spending the weekend at Balmoral.

A Buckingham Palace spokeswoman said: "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."

Asked whether the Royal Family intended to take part in any public services commemorating the anniversary, she said: "The Royal Family recognises that people may want to remember the princess in any number of different ways, but they want to remember Diana privately with Princes William and Harry."

The prayer service at Althorp will be held the day after the house, home of the Spencer family for 500 years, closes to the public to allow the family to mark the day in private.

Earl Spencer will be joined by Lady Jane Fellowes, Lady Sarah McCorquodale and their families for the service at Althorp House, near the village of Great Brington in Northamptonshire.

A day of quiet contemplation will mark the anniversary

Diana's mother, Mrs Frances Shand-Kydd, has yet to decide how she will mark the day, but she "has expressed the desire to spend the day alone," a spokeswoman for Althorp said.

A spokeswoman for the Diana, Princess of Wales Memorial Fund said no plans for events on August 31 had been put forward to it for approval.

She said: "No one has approached us as yet, and we don't really expect anything now, so late on."

She said a fund-raising 'pilgrimage walk' through London, partly along the route of the Princess's funeral, was planned - but a week before the anniversary.

A spokeswoman for the Department of Culture, Media and Sport also said she knew of no events planned for the day.

It had been hoped that plans for a remembrance garden for the Princess in Kensington Gardens, west London, could be formally announced on or around August 31.

But after local residents strongly criticised the idea earlier this week, even this seems in doubt.