At last, what Stella McCartney really thinks of her step-mother

With her video camera trained on waiting cameramen, yesterday was just like any other day for Heather Mills-McCartney. On the day her daughter Beatrice celebrated her third birthday, Lady McCartney kept up her daily ritual of chronicling encounters with the media on video as she drove from her East Sussex home.

But there was one encounter she didn't capture on film: the broadside everybody in the McCartney saga had been anticipating, as Sir Paul's outspoken fashion designer daughter Stella finally broke the family's silence and disclosed exactly what she thought of her soon-to-be-ex stepmother.

Stella, 34, who is heavily pregnant, reportedly screamed "I'll kill the bitch" in a confrontation at the family home last week, after learning that Heather had accused Sir Paul of hitting her mother, Linda, during their marriage. Stella allegedly said: "I told you she was a bitch. Why did you marry her? She's been a manipulative cow from day one. The cow won't be happy until she destroys all of us ­ and our memories of our mother."

The quotes, made public in The News of The World today, will fuel acrimony in the multi-million pound divorce. The newspaper quotes a source close to the family claiming Stella compared her stepmother to "a pile of vomit". The source said: "Stella would get so upset listening to her dad that she once said, 'I don't want to bring my child into the world with her as a grandmother. She's a bitch from hell.'"

The newspaper claims that Stella told Heather she considered her "a money-grabbing bitch", and that Sir Paul, 64, was now drinking heavily as a result of the events surrounding his divorce and the effect it was having on his family.

In a separate development, it was claimed last night that Heather is planning a Princess Diana-style "tell-all" primetime TV interview, and is in negotiations with the BBC and ITV.

Beatrice had a low-key birthday party at a children's activity centre in East Sussex yesterday afternoon. By contrast, her father will raise his profile significantly in a few days' time before a packed house at the Royal Albert Hall. His classical work, Ecce Cor Meum ­ "Behold My Heart" ­ receives its premier. The audience is expected to include P Diddy, Tony Bennett and possibly Madonna, a friend of Stella.

This is Sir Paul's first major public outing since his divorce descended into mud-slinging and acrimony after court papers alleging he was cruel and occasionally violent were leaked. It will also be a pointed rebuff to Heather; the work was eight years in the making and is dedicated to his first wife, Linda, who died in 1998 from breast cancer.

He will get through this moment of scrutiny with the help of family and friends: Sir Paul will be seated in one of the velvet-draped boxes beside Stella and his other children James and Mary. Others in the audience will include friends and supporters such as Kate Moss and the musician and TV presenter Jools Holland. "It will undoubtedly be a very poignant occasion. Everyone will be rallying round," said an insider.

The hostile relationship between the former Beatle and his wife, dubbed Lady Mucca by The Sun, plummeted to new depths just under a fortnight ago when the court papers apparently prepared by Heather were leaked. The pages were sent anonymously to the Press Association news agency's head office in Howden, East Yorkshire. The company's IT team has traced the source of the original fax to a newsagent in central London, Drury News, whose proprietor claimed to remember a brunette woman sending the fax.

It has also emerged that Heather's PR adviser, Phil Hall, has been sidelined from handling the minutiae of the case in favour of the PR Office, the firm that looks after the account for her lawyers, Mishcon de Reya.

In an interview this week with USA Today, Sir Paul, who has been attending rehearsals of Ecce Cor Meum, said he was still hoping for a peaceful outcome. "I'm just hoping for a happy resolution, particularly for the sake of our beautiful daughter, Beatrice, and my other children," he said.