A serving police superintendent with City of London Police has been arrested on suspicion of passing unauthorised information to a journalist.
The officer was arrested by the Independent Police Complaints Commission (IPCC) on suspicion of misconduct in a public office.
He was arrested after Metropolitan Police officers investigating payments by journalists to public officials passed information to the IPCC.
In a statement, the IPCC said: "A serving officer of superintendent rank, from City of London Police, has today been arrested by the Independent Police Complaints Commission (IPCC) on suspicion of misconduct in public office.
"The arrest is the result of information passed to the IPCC by the Metropolitan Police Service team investigating Operation Elveden.
"It relates to the alleged passing of unauthorised information to a journalist.
"The man is currently in custody at a London police station."
Operation Elveden, Scotland Yard's investigation into allegations of inappropriate payments to police, is being supervised by the IPCC.
It began last summer after officers were handed documents suggesting News International journalists made illegal payments to the police.
Elveden is linked to Operation Weeting, the investigation into phone hacking, and Operation Tuleta, a probe into allegations of computer hacking.
Deputy Assistant Commissioner Sue Akers, of the Metropolitan Police, is leading all three investigations.