By TOM KELLY

Last updated at 22:00 28 February 2008

Phone lines were tampered with at a house where Prince Charles is believed to have had secret liaisons with Camilla Parker Bowles while still married to Diana, it was revealed yesterday.

The discovery prompted fears of widespread bugging of the Royal Family and led to high-level talks involving the heads of MI5 and GCHQ, the Government's listening station, during the early 1990s, the Diana inquest heard.

Details of the tampering emerged during a secret investigation into the recording of Charles's highly intimate late-night mobile phone conversation with Camilla in 1989.

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A transcript of the "Camillagate" call was made public in 1992, weeks after news had broken about the "Squidgygate" tapes involving Diana and James Gilbey.

It caused huge embarrassment to the Royal Family as it included details of how the prince had told his lover that he wanted to be her "tampon".

Yesterday, minutes from a security meeting describing the inquiry into the Camillagate scandal were read to the London hearing into the death of Princess Diana and her lover Dodi Fayed.

Lord Fellowes, who was then the Queen's private secretary, told the gathering in April 1993: "Evidence had been found that the fixed telephone lines had been tampered with.

"It was almost certain that this was the location where the Prince of Wales had been staying on the night of the alleged conversation between him and Mrs Parker Bowles."

The location was not named, but it is thought to be Eaton Hall in Cheshire, home of Charles's great friend, the Duke of Westminster.

The prince is thought to have enjoyed clandestine meetings with Camilla at the house.

The inquest heard that Charles made the call to Camilla, who was at her home in Wiltshire, on a mobile phone, not a landline.

But the minutes from the meeting showed that Sir Robin Butler, the then Cabinet Secretary, was so concerned about the tampering that he asked whether all royal premises should be checked for listening devices.

The latest revelations emerged as Sir John Adye, the head of GCHQ from 1989 to 1996, gave evidence.

He dismissed claims that the service was bugging the royals and said it was "nonsense" to suggest that they were behind the Camillagate and Squidgygate tapes.

Under the law GCHQ would have needed to get the Foreign Secretary to sign off such a phone tap, which the agency had not sought, he said.

Ian Burnett QC, for the coroner, said: "And intercepting the Royal Family is simply not within the scope of the intelligence the government was seeking?"

Sir John replied: "Indeed, it was not." The inquest continues.