The senior officer was held by investigators from the Independent Police Complaints Commission, who have powers of arrest.
The IPCC said the arrest came as a result of information passed on by Scotland Yard's Operation Elveden, which is investigating alleged corrupt payments to public officials.
It is understood that the arrest was carried out by the IPCC, rather than Scotland Yard itself, because the allegation did not involve the officer in question being paid for information, meaning it falls outside the remit of Operation Elveden.
The Metropolitan Police would only say the arrest was "not part of Operation Elveden".
The officer is currently in custody at a London police station, where he is due to be questioned on suspicion of misconduct in a public office.
City of London Police declined to comment on the arrest.
