Glenn Mulcaire, the private detective who worked for the News of the World, has been arrested in connection with phone hacking and perverting the course of justice.
Officers from Scotland Yard's Operation Weeting said a 41-year-old man was arrested at an address in London on suspicion of conspiring to intercept voicemail messages.
He was being held in custody at a south London police station, a spokesman said.
The Scotland Yard spokesman said: "On December 7, 2011 officers from Operation Weeting arrested a man in connection with phone hacking and perverting the course of justice.
"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."
Scotland Yard's phone-hacking squad is working its way through 300 million emails from News International.
Detectives investigating phone hacking have 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.
Mulcaire was the investigator responsible for gaining access to the voicemails of a number of celebrities in order to feed stories to the News of the World.