Until now, the officers involved in 'Operation Weeting' have been reviewing evidence seized in the original 2006 investigation
On the rare occasions that police officers appear in newspaper offices, they are usually guests of the editor.
Now the Metropolitan Police have entered the News of the World newsroom to search a desk belonging to a high-ranking reporter, Neville Thurlbeck. Such visits are so rare as to be virtually unprecedented, but this is the second time Scotland Yard has arrived at the paper to carry out a search.
Five years ago paperwork belonging to former royal editor Clive Goodman was seized by the Met during its original inquiry into phone hacking at the title. Until now Goodman, jailed in January 2007, was the only News of the World journalist to be arrested for listening to private voicemail messages.
Thurlbeck is the most senior reporter at the News of the World, responsible for a string of scoops under a series of editors, including Rebekah Brooks, who is now chief executive of the paper's parent company, News International.
He was news editor at the paper before returning to his previous job as chief reporter in 2003, the year Andy Coulson succeeded Brooks as editor. He broke the story that former Formula One President Max Mosley took part in sadomasochistic orgies and revealed that Jeffrey Archer had relied on a false alibi in an infamous libel case, a story that resulted in the prominent Conservative peer and novelist being jailed for perjury.
Thurlbeck was arrested after walking into a police station in south-west London. Ian Edmondson, sacked as the paper's assistant editor (news) in January, was also arrested in a different location. Both men were released without charge but the fact two senior News of the World figures - one past, one present - were detained signals that the new police inquiry into phone-hacking allegations at the paper is entering a new phase.
Until now, the 40 or so officers involved in "Operation Weeting" have been reviewing evidence seized in the original 2006 Scotland Yard investigation, still in the Met's possession, and notifying high-profile victims that they were targeted by Glenn Mulcaire, a private investigator employed by the paper. They include the former deputy prime minister John Prescott, who had previously been repeatedly assured by senior Scotland Yard figures that he was not a victim. The Met has also interviewed other alleged victims of the practice who discovered since the original police inquiry they may have been targeted by Mulcaire in 2005 and 2006, when he was at his most prolific, after they launched legal proceedings against the paper.
Many of them, including Sienna Miller, Steve Coogan and former Sky commentator Andy Gray, had to obtain court orders forcing the Met to hand over copies of pages from Mulcaire's notebooks, which are still in the Met's possession.
They claim that evidence proves Mulcaire conspired with executives at the paper to routinely listen to private messages left on their mobiles.
The arrests demonstrate Scotland Yard is taking a more proactive approach as it attempts to prove to its critics that it can be trusted to root out wrongdoing at the paper.
Stung by allegations that it failed to notify hacking victims and embarrassed by its acceptance that the hacking plot was the work of Goodman alone, the Met's acting commissioner Tim Godwin has pledged to leave "no stone unturned" in its latest investigation.
Only one News of the World journalist, former royal editor Clive Goodman, has been convicted of a crime. Several others have been questioned. Thurlbeck was interviewed last year.
The paper's parent company, Rupert Murdoch's News International, maintains it will not tolerate wrongdoing among staff and will act when presented with evidence its reporters have acted unlawfully. Insiders say they co-operated with police, who did not arrive at the paper's new east London offices "mob-handed" and went about their business with the minimum of fuss.
Sources close to police, however, contend that executives at the paper made it clear they were unhappy about the Met's presence, which was an unexpected as it was unwelcome. It is understood that items were removed form Thurlbeck's desk. Thurlbeck denies acting illegally.
Edmondson also insists he is innocent of any crime. But his sacking in January, after Mulcaire named him in court documents as the man who ordered him to hack into a phone belonging to football agent Sky Andrew, was the moment the paper's "rogue reporter" defence collapsed.
When Goodman was jailed the paper insisted he had acted alone. After Edmondson was named in court documents, the paper effectively adopted a "rogue executive" defence, accusing him of lying about his dealings with Mulcaire when quizzed about his relationship with him in the past. Thurlbeck's arrest does not signify that the police possess any evidence that would implicate more senior executives at News International in the scandal.
In that sense, the "rogue executive" defence, which can be cited regardless of how many reporters – senior or otherwise – are arrested, questioned or even charged by the police, remains intact. As long as it survives, senior News International figures who have not been accused of wrongdoing, up to and including chairman James Murdoch, can afford to take a relaxed view of the ongoing inquiry, even when officers turn up at the News of the World offices at short notice.