Five suspects arrested over allegations of cover-ups in the phone-hacking inquiry - understood to include Rebekah Brooks and her racehorse trainer husband - have been released on bail, Scotland Yard said.
Mark Hanna, News International's head of security, was also confirmed by the company as one of the six people arrested in raids in Oxfordshire, London, Hampshire and Hertfordshire.
A spokesman for Scotland Yard said they were bailed to dates next month while the sixth suspect remains in custody.
The dawn raid on the Brooks' home is potentially embarrassing for David Cameron, who was forced to make further admissions earlier this month about the extent of his relationship with the couple.
After it emerged that Scotland Yard lent an ex-police horse, Raisa, to Mrs Brooks, the Prime Minister conceded it had been among his mounts on rides with Mr Brooks - a friend from their Eton schooldays.
Officers from Operation Weeting - the inquiry into voicemail interceptions - said they consulted the Crown Prosecution Service before carrying out their busiest morning of arrests since the operation was launched last year.
Mrs Brooks, 43, was questioned at an Oxfordshire police station while Mr Brooks was interviewed at a Buckinghamshire police station, the Press Association reported.
The force said searches were going on at several addresses after a 39-year-old man was arrested in Hampshire, a 46-year-old man was held in west London, a 38-year-old man was arrested in Hertfordshire and a 48-year-old man was detained at a business address in east London, and were also interviewed at separate police stations.
The 38-year-old man remained in custody at a central London police station on Tuesday evening.
The arrests, which are not understood to result from information passed to them by News Corporation's management and standards committee, come just days after Mrs Brooks's lawyer Stephen Parkinson said evidence given by Metropolitan Police deputy assistant commissioner Sue Akers at the Leveson Inquiry brought "much prejudicial material" into the public domain.
Mr Brooks, who writes for the Daily Telegraph, described in his column on Monday the pubs he would visit as part of his outing to the Cheltenham Festival.
He wrote in the paper: "The happiest moment of my year is about three hours before the first race at Cheltenham on Tuesday."
Mrs Brooks was previously arrested and questioned by appointment last July, days after resigning as chief executive.
But her relations with top police officers and politicians were called into question in recent weeks after it emerged she "fostered" Raisa the horse when it retired from active service in 2008.
She paid food and vet bills until Raisa was rehoused with a police officer in 2010, months before fresh investigations began into illegal activities at the News of the World.
Mr Cameron, asked whether the horse riding was emblematic of his over-close ties with Mrs Brooks, said: "I have known Charlie Brooks, the husband of Rebekah Brooks, for over 30 years.
"He is a good friend and he is a neighbour in the constituency. We live a few miles apart."
Asked about the arrest, a Downing Street spokeswoman said: "The Prime Minister is travelling to Washington. It is an operational matter for the police. You wouldn't expect him to comment on it."
The Scotland Yard deputy assistant commissioner, who is leading the investigation into illegal news-gathering, told the inquiry into press standards that there was a "culture of illegal payments" at the Sun newspaper.
Ms Akers, who is in charge of three linked inquiries into phone hacking, illicit payments and computer hacking, told Lord Justice Leveson the payments appeared to have been authorised at a "senior level".
This week it was announced that the Attorney General is looking into concerns that the policewoman could have prejudiced any potential trials.
A total of 22 people have now been arrested under Weeting, which has been running since January last year, Scotland Yard said.
A Scotland Yard statement said earlier: "The co-ordinated arrests were made between approximately 5am and 7am this morning by officers from Operation Weeting, the MPS (Metropolitan Police Service) inquiry into the phone hacking of voicemail boxes.
"All six - five men and one woman - were arrested on suspicion of conspiracy to pervert the course of justice, contrary to the Criminal Law Act 1977.
"A number of addresses connected to the arrests are being searched. Today's operation follows consultation with the Crown Prosecution Service."