Rebekah Brooks was arrested in a dawn raid at her Oxfordshire home yesterday as Scotland Yard's inquiry into phone hacking moved into a dramatic new phase of investigating a possible cover up at the top of Rupert Murdoch's British newspapers.

The 43-year-old former editor of The Sun was one of six people, including her husband, the racehorse trainer Charlie Brooks, detained by detectives from the Yard's Operation Weeting on the serious charge of suspected conspiracy to pervert the course of justice. All six were subsequently released on bail last night.

The arrests, which took place between 5am and 7am and followed consultations with the Crown Prosecution Service, are a significant escalation in the gravity of the offences being considered by police. Among those arrested were two current News International employees, including the head of security, Mark Hanna.

The Independent understands police now believe there may have been a plot to conceal the extent of voicemail interception at the NOTW after the launch of Weeting 14 months ago. Detectives are believed to be investigating the NI's handling of sensitive data relating to phone hacking, including the activities of staff during an arrest last year.

Mr Brooks had been looking forward to attending yesterday's opening of the Cheltenham Festival, writing that his anticipation of the first race was the "happiest moment of my year" in his Daily Telegraph column on Monday.

Instead, he and Scotland Yard's other targets were roused from their beds as officers began searching their homes before taking them in for questioning.

Mr and Ms Brooks were taken to separate police stations after being arrested at their farmhouse in Chipping Norton, Oxfordshire. David Cameron, a long-standing friend of Mr Brooks and part of the couple's social circle in the Cotswolds, distanced himself from the developments as he flew to America. A spokesman said: "It is an operational matter for the police."

Downing Street was last week forced to admit after days of dodging the issue that Mr Cameron had ridden Raisa, a horse loaned to Ms Brooks by the Met.

Ms Brooks resigned as chief executive of NI last July shortly before her arrest on suspicion of conspiring to hack voicemails and making illegal payments to police. Her spokesman declined to comment on the latest arrest, while Scotland Yard declined to discuss the reason behind the arrest of Mr Brooks.