Sir Paul McCartney angrily denied tonight that his estranged wife was a gold-digger only hours after announcing a separation that could leave her one of Britain's richest women.

Sir Paul and Lady McCartney - the former model Heather Mills - confirmed their split after four years of marriage in a statement that blamed "constant intrusion" into their private lives for ruining their relationship.

The split paves the way for what could be Britain's biggest divorce settlement. The former Beatle famously refused to sign a pre-nuptial agreement before the couple's wedding in 2002 but legal experts said the separation could easily end up costing him £200 million, or a quarter of his fortune.

In a message posted on his website this afternoon, Sir Paul rejected suggestions that Lady McCartney had married him "for the money" and pointed out that she had spent her life campaigning for charity without earning a penny.

"I’m really disappointed that during a very difficult and emotional time for both Heather and myself there are certain people in the media who are writing things about Heather that are just plain untrue," he said.

"It’s been suggested that she married me for the money and there is not an ounce of truth in this. She is a very generous person who spends most of her time trying to help others in greater need than herself.

"All the work she does is unpaid so these stories are ridiculous and completely unfounded."

Sir Paul, 64 next month, met Ms Mills - who is 26 years his junior - at an awards dinner in 1999, the year after his first wife, Linda, died of cancer. They married in a lavish ceremony in an Irish castle in June 2002 and had a daughter, Beatrice, the following year.

The pair met through Ms Mills's charity work for the Heather Mills Health Trust, recycling prosthetic limbs and campaigning against landmines. She formed the charity after losing a leg when she was knocked down by a police motorcyclist in 1993.

Confirmation of their separation follows weeks of media speculation about the state of their marriage. The couple are thought to have been living at separate addresses in recent weeks - Sir Paul on the family farm in Peasmarsh, East Sussex, and his wife at their home in Hove, about 50 miles away.

There have long been reports that Lady McCartney, 38, failed to hit it off with Sir Paul's three children from his first marriage, especially the fashion designer Stella McCartney.

But in their statement today, the couple blamed their marriage break-up on the pressure of living in the public gaze and intrusive media attention.