Heather Mills-McCartney raised the stakes in her divorce from Sir Paul McCartney today by hiring the solicitor of Diana, Princess of Wales.

Anthony Julius, a senior partner at London law firm Mishcon de Reya, will represent Lady McCartney as she negotiates a settlement with her husband of four years. The solicitor will face Fiona Shackleton, of Payne Hicks Beach, who represented the Prince of Wales in the royal divorce ten years ago.

Mr Julius, dubbed Anthony Genius by colleagues, reportedly won a £17 million deal for the Princess in 1996. It is understood that his work with the Princess was the solicitor-advocate’s only other divorce case. Mr Julius specialises in media law and has represented a string of high-profile clients including the newspaper proprietor Robert Maxwell.

The two legal teams will be battling over Sir Paul’s fortune, which is believed to be more than £800 million. It has been reported that Lady McCartney could receive as much as £200 million.

The news came as a source close to Sir Paul dismissed stories that songwriter had deliberately locked his wife out of his London home as "rubbish". Police were called to the home of the former Beatle after a person - reported to be his estranged wife’s security guard - was found on the premises.

Lady McCartney and the couple’s daughter, Beatrice, had been shut out of the house in St John’s Wood, north-west London, after the locks were changed, it was reported. After her driver tried the intercom and got no answer her security guard scaled the wall. Fearing he might be an intruder, members of Sir Paul’s staff called the police and officers went to the address.

A Scotland Yard spokesman said: "Police were called at approximately 7.50pm yesterday to an address in NW8 to reports of a suspect on the premises. Officers attended and spoke to a female who subsequently left the scene. No offences took place."

Last month it was confirmed that Sir Paul had begun formal divorce proceedings and it was reported that he cited his wife’s "unreasonable behaviour" in the documents.

When the couple revealed they would split in May they had insisted their separation would be amicable but they admitted that doing so under media scrutiny and with a two-year-old child would be "immensely stressful".

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