Police said on Saturday they were searching the London offices of Rupert Murdoch's News International and had arrested four people, including a policeman, in an investigation into suspected payments to police officers for information.
The probe is linked to a continuing investigation into phone hacking at the now-closed News of the World tabloid, published by News International, the British arm of Murdoch's News Corp media empire.
Saturday's operation was the result of information passed to police by News Corp's Management and Standards Committee, set up in the wake of the phone hacking scandal, London's Metropolitan Police said.
One of those being questioned on suspicion of corruption was a 29-year-old police officer serving with the Met Police's Territorial Policing Command, who was arrested at the central London police station where he worked.
The others, all arrested at their homes, were a 48-year-old man from north London and two men from Essex, east of the capital, aged 48 and 56.
Searches at News International's offices in Wapping, east London, and at the arrested men's homes, were expected to continue until the afternoon, police said.
The operation takes to 12 the number of arrests in a probe into allegations journalists paid police in return for information, known as Operation Elveden, one of three criminal investigations into the news-gathering practices of the News of the World.
Last week, News International settled a string of legal claims after it admitted that people working for the tabloid had hacked in to the private phones of celebrities and others to generate stories.
The phone hacking scandal drew attention to the level of political influence held by editors and executives at News International, and other newspapers in Britain.
It embarrassed British politicians for their close ties with newspaper executives and also the police, who repeatedly failed to investigate allegations of illegal phone hacking.
News International had no immediate comment on Saturday's police operation, a spokeswoman for the media group said.
(Additional reporting by Michael Holden; Editing by Rosalind Russell)