A woman has been arrested by Scotland Yard's counter-terrorism command on suspicion of an offence under the Official Secrets Act.
The Metropolitan Police said the 65-year-old woman, who is contracted to carry out work for a government department, was arrested at an address in north London on Wednesday by officers "acting upon intelligence received".
She was arrested on suspicion of an offence contrary to section 1 of the Official Secret Act 1911, and was detained under the Police and Criminal Evidence Act.
The woman is in custody at a south London police station.
Officers are also carrying out a search at an address in north London as part of the investigation.