Former News of the World chief reporter Neville Thurlbeck was rearrested today by detectives investigating phone-hacking.
Thurlbeck was one of the first suspects questioned by Operation Weeting detectives last April.
Detectives detained him a day after former Sun editor Rebekah Brooks, her husband Charlie, and four other suspects were arrested over allegations of cover-ups surrounding the inquiry.
Mr Thurlbeck was being questioned tonight on suspicion of witness intimidation and encouraging or assisting an offence.
He has blogged about the inquiry in recent months and claimed that he refused a police offer to give evidence against his ex-employer News International.
A Scotland Yard statement said: “A 51-year-old man was arrested by appointment at a central London police station at approximately 4pm today by officers from Operation Weeting, the MPS inquiry into the phone hacking of voicemails.
“He was arrested on suspicion of intimidation of a witness (contrary to Section 51 of the Criminal Justice and Public Order Act 1994) and encouraging or assisting an offence (contrary to Section 46 of the Serious Crime Act 2007).”
Thurlbeck was previously arrested on April 5 on suspicion of conspiring to intercept communications and unlawful interception of voicemail messages.
The force added: “He is bailed to return to a south west London police station in May this year in relation to the arrest in April.”
Mr Thurlbeck said detectives asked him to become a prosecution witness after seizing documents from his home.
Evidence taken from his property after his first arrest last April indicated that he warned senior colleagues two years ago about hacking, he said.
Mr Thurlbeck said detectives hoped he would become a key witness in return for potential immunity from prosecution.
But he said he had turned down the offer.
Mr Thurlbeck said in November: “I have informed Scotland Yard that while I fully understand and respect the reason for their request of me to give evidence for the Crown in any prosecution arising from Operation Weeting, it is my opinion that a detailed and forensic inquiry into my working methods by what is a highly professional police unit will fully exonerate me.
“So, on that basis, I have declined their offer.”
Mr Thurlbeck has also previously lodged a claim for unfair dismissal against News International.
Mr and Mrs Brooks were bailed yesterday along with Mark Hanna, News International’s head of security, and three other suspects questioned on suspicion of conspiracy to pervert the course of justice.
The dawn raid on Mr and Mrs Brooks’s 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.