The royal editor of News of the World and two other men have been arrested over a plot to tap phone calls from Prince Charles's household.

Police have now widened their investigation in the belief that the calls of other public figures beyond the Royals, including an MP, have also been intercepted.

The inquiry started last December after three staff members at Clarence House, the official residence of the Prince, told the Met's royal protection unit of fears that their mobile phone conversations were being tapped.

Detectives have also not ruled out the possibility that other royal households, including Buckingham Palace, may have been targeted.

It is thought other victims included ministers, an MP, military chiefs, a leading media figure and celebrities - but not the prime minister.

Officers from the anti-terrorist branch became involved over the "potential security implications".

Clive Owen, 48-year-old royal editor of News of the World, was arrested at his house in Putney at 6am yesterday. The Sunday tabloid confirmed the arrest.

Two other unnamed men, aged 35 and 50, were detained at their homes in Sutton, Surrey, yesterday morning. They are not journalists, but the Met would not confirm their occupations.

Although the 50-year-old has been released on police bail, police are still questioning the other two. Both their homes have been searched.

Other searches took place at the offices of News of the World in Wapping, east London, as well as businesses in Sutton and Chelsea.

The arrests were made under the Regulation of Investigatory Powers Act 2000, which bans unlawful intercepts.

Clarence House would not comment on the phone tap allegations.

In a statement, the Met said its inquiry focused on "alleged repeated security breaches within telephone networks over a significant period of time.

"As a result of their inquiries police now believe that public figures beyond the Royal Household have had their telephones intercepted, which may have potential security implications."

The former royal aide Dickie Arbiter said there was "a lot of sensitivity" in the royal family over phone taps after previous mobile phone interceptions.

In one incident, details of an intimate conversation said to be between Diana, Princess of Wales, and her long-standing friend James Gilbey were published. He allegedly called her "squidgy".