CNN star Piers Morgan was an extremely hands-on tabloid editor who must have known that phone hacking was rife at his paper, a former employee alleged Wednesday.

Business journalist James Hipwell said that voicemail interception was an everyday activity at the Daily Mirror, where he worked as a share tipster. Hipwell told a British inquiry into media ethics that while he had no direct evidence that the editor was involved in the practice, he said it was impossible to imagine that Morgan had been kept in the dark.

"Nothing happened at the newspaper without him knowing," Hipwell testified.

Hipwell and Morgan have a long history. Both were investigated as part of an inquiry into market manipulation after it emerged that Morgan had made a quick profit by buying shares which were promoted in the next day's edition of the paper.

Morgan was cleared of wrongdoing, but Hipwell and another tipster, Anil Bhoyrul, were convicted in 2005. Hipwell said that he always believed that his former boss had been as guilty as he was.

"I can understand why people think that I have an axe to grind against him," Hipwell told the inquiry.

Meanwhile authorities said that they had arrested their first serving police officer as part of an investigation into bribes paid out by the country's journalists.

London police said that the 52-year-old woman, who has not been identified, was arrested in the early morning on suspicion of corruption and misconduct in a public office. The woman was detained at a house in Essex, in southeastern England, and is being questioned at a local police station.

Eight people, including a reporter working for The Sun tabloid, have so far been arrested as part of the police corruption inquiry, although no one has yet been charged.

The investigation is linked to police inquiries into tabloid phone and computer hacking.