Thames Valley Police officers raided the premises at Auckland Park at 11.35am on Tuesday and took a number of documents and a computer.

Later, police arrested a part-time member of the paper's reporting staff at the journalist's home on suspicion of aiding and abetting misconduct in a public office.

A Thames Valley Police officer and a Hertfordshire Constabulary officer were arrested on suspicion of misconduct in a public office.

A 52-year-old Hertfordshire man and a soldier from Cambridgeshire were also arrested on suspicion of aiding and abetting misconduct in a public office.

Police told Johnston Press, which owns the Citizen, they are investigating allegations of police corruption and the leakage of confidential police information.

In a statement the company said: "Johnston Press will co-operate with the police inquiries but has no grounds to suppose that its reporter was not carrying out journalistic responsibilities fairly and legally.

"To support its reporter, the company will fund independent legal advice."

A Thames Valley Police statement added: "The investigation relates to the leaking of sensitive police information and does not involve information relating to the army or any military operations.

"Two of the five people arrested were taken to a police station in Thames Valley where they were questioned. They have since been released on police bail.

"The two arrested by Hertfordshire Constabulary have also been released pending further enquiries."