So far, one person has been charged out of a total of 52 arrests as a result of Operation Elveden, the police probe into corrupt payments and other information leaks.
Detective Chief Inspector April Casburn is due to face trial in January accused of leaking information to the now-defunct News of the World about the police inquiry into whether to re-open the investigation into phone hacking.
Last week a retired police officer and former journalist became the first people arrested as part of the operation to be told they would face no further action.
Officials from the Prison Service and the Ministry of Defence, and a serving member of the armed forces, are among those questioned by Elveden detectives.
Operation Elveden is being run alongside two others: Operation Weeting, which is looking at allegations of phone hacking, and Operation Tuleta, an inquiry into accusations of computer hacking and other privacy breaches.
The Metropolitan Police has previously estimated that the investigations will cost around £40 million.