A private investigator previously employed by the News of the World was arrested today over allegations of phone hacking and perverting the course of justice.
Glenn Mulcaire is being held by Operation Weeting detectives after officers swooped on his Surrey home at dawn, sources said.
Scotland Yard said a 41-year-old was being questioned in custody at a south London police station.
Mulcaire, from Sutton, ran Nine Consultancy, a firm offering to protect clients from media intrusion, before landing work with the now axed Sunday tabloid.
He signed a year's contract with the paper for "research and information services" worth more than £100,000.
The suspect commented through his lawyer last month on allegations surrounding the hacking of a mobile phone belonging to murdered schoolgirl Milly Dowler.
Sarah Webb, of Payne Hicks Beach law firm, said: "Glenn Mulcaire has previously expressed his sincere personal sympathy for the Dowler family.
"Because of the on-going criminal investigation, it is not possible to say much at this time."
Pledging support to Surrey Police's agreement to disclose documents concerning interceptions in 2002, Ms Webb added: "He is confident that they will shed light on the actions he took then and the basis of them.
"Further, he confirms that he did not delete messages and had no reason to do so."
A Metropolitan Police spokesman said detectives were questioning a suspect over the phone interceptions and perverting the course of justice.
A statement from the force said: "At 7am officers arrested the man at an address in London on suspicion of conspiring to intercept voicemail messages, contrary to Section 1 (1) of the Criminal Law Act 1977 and on suspicion of perverting the course of justice contrary to common law. The man is currently in custody at a south London police station.
"It would be inappropriate to discuss any further details at this time."
Former footballer Mulcaire, who scored AFC Wimbledon's first ever goal in a friendly against Bromley in 2002, is the 18th hacking-related arrest since the fresh investigation was launched.
University lecturer Bethany Usher, 31, was questioned last week over her time working for the tabloid as Scotland Yard's phone-hacking squad works its way through 300 million emails from News International.
Detectives have also arrested a series of high-profile figures, including former News International chief executive Rebekah Brooks and ex-Downing Street communications chief Andy Coulson.
The scandal has already led to the closure of the News of the World after 168 years, prompted a major public inquiry, and forced the resignation of Metropolitan Police commissioner Sir Paul Stephenson and assistant commissioner John Yates.
Some 1,800 people have come forward to express fears that they may have been hacked.