A television reporter yesterday described the moment he and Prince William realised that the mobile phone voicemail messages of Royal aides could have been hacked into.
Tom Bradby, ITV's political editor, claimed details of a meeting he had arranged with the prince appeared in the News of the World before it had even taken place.
When he eventually met William and discussed the matter, the prince also raised concerns about another story that had appeared about a meeting with his knee surgeon.
They concluded that one of the ways these details could have got out was if mobile phone voicemail messages had been intercepted, he said.
The newspaper's royal editor Clive Goodman was being questioned last night along with another man by police over alleged security breaches involving the mobile phones of royal officials.
Scotland Yard's Anti-Terrorist Branch investigation is also examining whether other high profile public figures or members of the Royal Household had their voicemail messages hacked into.
At least one Cabinet Minister, but not the Prime Minister, is understood to have been among those affected along with high-profile celebrities, top footballers and other senior politicians.
Mr Bradby, a former ITV News royal correspondent, told the channel's lunchtime bulletin: "I was due to have a private meeting with William and I was pretty surprised to find that, not only details of the meeting but of what we were going to discuss pitched up in the News of the World the Sunday before.
"When he and I hooked up we both looked at each other and said, 'Well how on earth did that get out?' and we worked out that only he and I and two people incredibly close to him had actually known about it.
"Then we started discussing one or two other things that had happened recently. There had been a meeting he had had with a knee surgeon that again only he and his personal secretary and the knee surgeon had known about that had got into the News of the World.
"Basically, the answer we came up with was that it must be something like breaking into mobile answering machine messages."
Clarence House is the official residence of Prince Charles, his wife, the Duchess of Cornwall, and the Princes William and Harry.
The News of the World has so far not commented beyond its statement on Tuesday night confirming Mr Goodman's arrest.
Mr Goodman, 48, the newspaper's long-standing royal editor, was held at his home in Putney and was being questioned at Charing Cross police station.
A 35-year-old man arrested at his home in Sutton, south London, on Tuesday, is being held at a different station.
A third man, aged 50, also arrested in Sutton on Tuesday, was released on police bail early yesterday.
All three were held under Section 1 of the Regulation of Investigatory Powers Act 2000, under which the potential penalties are a maximum of two years in jail, a fine or both.
The investigation began in December last year after three members of the Royal Household at Clarence House contacted police.
Clarence House would not comment on reports that a voicemail sent to Paddy Harverson, the Prince of Wales's communications secretary, had been hacked into.
Detectives are investigating how long the alleged phone hacking has been going on for, amid claims that it could have been a year or more.
Sources denied that either Charles's or Camilla's phones were among those allegedly hacked into.
The allegations do not relate to the tapping of live telephone calls. The investigation is being handled by a small team of officers from Scotland Yard's Anti-Terrorist Branch because of the wider security implications of the allegations.
Former royal aide Dickie Arbiter said there was considerable sensitivity within the Royal Family over phone interceptions following the infamous "Squidgygate" episode in the 1990s, when details of an intimate telephone conversation between Diana and long-standing friend James Gilbey were published. The Prince of Wales, his wife Camilla were also the unwitting subjects of phone interception in 1993 when a tape, which came to be dubbed "Camillagate", of an intimate late-night phone call between them was made public.