Police have arrested a man on suspicion of leaking details of the cost of protecting VIPs.
The arrest is believed to relate to recent media stories which detailed the expenses claims of people employed to protect the likes of former prime minister Tony Blair.
Officers from the MPS Directorate of Professional Standards arrested the 27-year-old man on suspicion of breaching Section 5 of the Official Secrets Act.
Police said the man was a former contractor to the Metropolitan Police.
He was arrested at work in central London on Friday and is in custody at a nearby police station.