Rebekah Brooks's phone was hacked 'at least 20 times'

She became the subject of media interest in her personal life when she was arrested for an alleged assault on her then husband

Rebekah Brooks, the chief executive of News International and former editor of The Sun, has been shown evidence suggesting her phone was hacked more than 20 times by a private investigator employed by another Rupert Murdoch title, it emerged last night.

News International confirmed the 43-year-old media executive met detectives last week from Operation Weeting – Scotland Yard's third investigation into phone hacking – to see records showing she was targeted by Glenn Mulcaire, the private detective employed by the News of the World to eavesdrop on the voicemails of numerous public figures.

The alleged hacking took place between 2005 and 2006, when Ms Brooks, who is also a former editor of the NOTW, was in charge of The Sun, and raises the question of whether Mr Mulcaire was at the centre of an effort by Britain's top-selling Sunday newspaper to spy on its daily stablemate.

The revelation that Ms Brooks was a likely repeated target for Mr Mulcaire was made by Sky News, whose largest shareholder is Mr Murdoch's News Corp. In a blog, the broadcaster's City editor, Mark Kleinman, suggested the hacking could also have been done by the private investigator on behalf of a rival newspaper.

Before his arrest in August 2006, Mr Mulcaire was employed on an exclusive contract with the NOTW worth £104,000 a year to supply "research and information services". No evidence has been produced to show that the amateur footballer-turned-private detective was working for titles outside News International.

The reason why Ms Brooks, who edited The Sun between 2003 and 2009, had her voicemails intercepted was unclear, though she became the subject of media interest in her personal life in November 2005 when she was arrested for an alleged assault on her then-husband, the actor Ross Kemp. She was released without charge.

Sky News reported that legal advisers to the News International chief executive, who has always denied any knowledge of phone hacking, were considering whether to apply for a court order requiring the Yard to hand over copies of the evidence found in Mr Mulcaire's documents.

A News International spokeswoman said: "We can confirm that Rebekah Brooks was recently shown documents by the police that proved she was a victim of illegal voicemail interception." It was unclear last night whether Ms Brooks would consider joining the list of high-profile individuals suing the NOTW for breach of privacy.

In a sign that the revelations may be damaging Mr Murdoch's popularity, it appears his annual summer party is no longer the hot ticket it used to be. As the media mogul stands on the verge of achieving his dream of taking complete control of the BSkyB satellite broadcasting empire, an invitation to last night's grand bash at the ornate Orangery, in the grounds of Kensington Palace, west London, drew more refusals than acceptances.

The Culture Secretary, Jeremy Hunt, who is set to announce whether the BSkyB deal can go through, has decided not to attend the party for fear that his presence might be misinterpreted. His colleague Ed Vaizey, the Culture minister, is also expected to be give it a miss. Liberal Democrat MPs, who attended in strength with Nick Clegg last year, are also likely to be conspicuously absent as the parliamentary party is attending an annual away day.

The Independent understands the event was also expected to be less star-studded than in previous years. Downing Street would not confirm whether David Cameron was attending, as he did last year with his wife, Samantha.