Just when it seemed Sir Paul McCartney's divorce from Heather Mills could not get any messier, Kate Moss joined the fray today.

The supermodel, and best friend of Sir Paul's daughter Stella, is said to be willing to testify in support of the former Beatle in the legal battle for his £825 million fortune.

See more pictures from the masked ball here

Masked and dangerous - read Tom Teodorczuk's blog here

Moss is reported to have told Stella she does not believe Ms Mills's claim of being forced to crawl to the bathroom at night because her husband refused to buy her an antique bedpan. Ms Mills, who lost a leg in a traffic accident, made the allegation in divorce papers, subsequently leaked to the press.

However, Moss, 32, is said to have told Stella the claims are "utter bullshit". A friend of Moss was quoted in the Sun today claiming: "Kate reassured Stella that she had seen her [Ms Mills] hopping around. She said she was 'jumping around like a f****** gazelle' and is prepared to swear to it, in court if necessary."

The source added: "Kate has met Heather and has seen her with the prosthetic limb on and off."

Yesterday Ms Mills, 38, announced she was suing the Daily Mail and the Evening Standard, and planned to take legal action against the Sun. She has accused Sir Paul of being violent on four occasions, claims the 64-year-old vigorously denies.

Last night Moss was out with boyfriend Pete Doherty at a Moët & Chandon masked ball in tribute to fashion photographer Nick Knight. The Babyshambles singer was on his best behaviour after Monday's fracas in Rome, when he fought a photographer after a concert and ended up covered in blood.

At the party in Strawberry Hill House, Twickenham, the 27-year-old and Moss serenaded each other in the karaoke room, singing Come Together by The Beatles, Close To You by The Carpenters and Itchycoo Park by The Small Faces. Both wore masks made by designer Philip Treacy - Moss's was one-eyed with a golden floral design, while Doherty had a black death mask.

Scarlett Johansson, who is in England filming historical drama The Other Boleyn Girl, arrived with French fashion designer Roland Mouret and New York club tycoon Amy Sacco. The actress said: "I'm having a lot of fun tonight."

Other guests included Elizabeth Jagger (in a harlequin leotard) and her mother Jerry Hall, designers Alexander McQueen and Ozwald Boateng, and models Erin O' Connor and Lily Donaldson.

With most guests adhering to the mask dress code, the party resembled a cross between Stanley Kubrick's 1999 film Eyes Wide Shut and Hello! Magazine.