Rebekah Brooks was questioned by Scotland Yard detectives yesterday about alleged corrupt payments to Ministry of Defence officials.
The former chief executive of News International was tackled on the subject of the alleged bribes when she answered bail for her arrest last July.
Mrs Brooks' spokesman refused to discuss details but a source close to the investigation said: "She was returning to answer bail in Milton Keynes this morning and was asked details about confidential sources for the Ministry of Defence. She was not asked about any other matters."
Mrs Brooks was first arrested by the Metropolitan Police in July last year on suspicion of phone hacking and corruption. Two days after she stepped down from running Rupert Murdoch's British newspaper group.
She was re-arrested last week at her home in Oxfordshire, along with her husband Charlie, a former racehorse trainer and friend of the Prime Minister, David Cameron. The couple, and four other individuals including News International's head of security, Mark Hanna, were held on suspicion of perverting the course of justice.
Those arrests suggested Scotland Yard was moving its focus from voicemail interception to a possible cover-up at News International headquarters in Wapping, east London.
As Scotland Yard has stepped up its investigation into the News of the World and The Sun, Mr Murdoch's New York-based holding company, News Corporation, has distanced itself from previous wrongdoing by passing information about allegedly inappropriate payments from The Sun to the Met's anti-bribery inquiry, Operation Elveden.
A third Scotland Yard inquiry, Operation Tuleta, is investigating allegations of computer hacking involving newspapers dating back more than 20 years.
A total of 169 detectives and support workers are staffing the three inquiries.
Last month, Sue Akers, the Met's Deputy Assistant Commissioner, said evidence passed by the MSC suggested The Sun had been running a "network of corrupted officials" across the police, government, defence, military and health service. In the past six months her officers have arrested 11 Sun journalists, the last of which was The Sun's defence editor, Virginia Wheeler, on 1 March.
In her appearance before the Leveson Inquiry on 27 February, Ms Akers said the evidence indicated that the inducements being offered to officials ran into tens of thousands of pounds. She added that the information they elicited appeared mostly to be "salacious gossip" rather than stories of genuine public interest and that journalists making payments appeared to know they were illegal, stressing the need for "care" and "cash payments".
A spokesman for the Metropolitan Police said last night: "A 43-year-old woman returned on bail today and was questioned at a police station in Buckinghamshire by officers from Operation Elveden. She has been rebailed to return to a London police station on a date in May pending further inquiries."Reuse content