The congregation at a memorial service in St Martin-in-the Fields church in central London will sing Let It Be as they say farewell to Linda, who died aged 56 after a long battle against breast cancer. The song was originally written by McCartney in honour of his mother, who also died of breast cancer when he was 14.

George Harrison...last seen in public with McCartney in 1969

Reports said the three surviving Beatles would reunite to perform Let It Be together, but a spokesman for Sir Paul said it would not happen.

Sir Paul, supported by his children, Heather, 36, Mary, 27, fashion designer Stella, 26, and James, 21, will address the congregation to pay tribute to the woman who was his wife for 30 years.

He has organised the service and said it should be as much a celebration of Linda's life as a mourning of her passing.

Musicians, photographers and animal rights campaigners will join the McCartney family and friends of the American-born former rock photographer who became a symbol of vegetarian and animal rights campaigns.

The service is invitation-only and the guest list is a Who's Who of British rock and pop. Elton John, who will be joined by Sting, Peter Gabriel and Pete Townshend, delayed plans to fly out of Britain so he could attend.

He said: "Linda was always very kind to me and she was a special person. Out of respect to her family I want to be there."

Hundreds of animal activists will hold a candlelit vigil in nearby Trafalgar Square. Some are coming by coach from Germany, Italy and France.

Ringo Starr

The animal rights group People for the Ethical Treatment said in a statement: "Linda inspired a generation with her activism, much as her husband inspired people with his music."

Writer Carla Lane, a close friend of Linda's, will represent the animal rights lobby at the service.

'Celebration of Linda's life'

She said: "There will be a brief mourning and then a celebration of Linda's life. Paul does not want it to be a morbid affair."

Joanna Lumley, another friend and fellow animal rights campaigner, will also address the congregation.

People will be able to write messages on a pair of eight-foot wings, which will be handed over to the McCartney family.

Linda McCartney was one of the world's most famous animal lovers

Linda, who died at a remote ranch in her native United States, had been seen only rarely in public since she developed cancer.

Her ashes have been scattered around the family's farmhouse home in East Sussex.

Sir Paul was recently photographed lighting a candle and meditating in Notre Dame Cathedral when he visited Stella in Paris.