A 65-year-old woman working at a government department has been arrested under the Official Secrets Act for being allegedly involved in espionage activities.

Although the arrest was carried out by Scotland Yard’s counter-terrorism officers the investigation, according to Whitehall sources, relates to alleged supplying of classified information to another state or organisation rather than terrorism.

The detained woman, from North London, was employed on a contract. She was not, it is believed, working for any of the security agencies.

The arrest took place under Section 1 of the 1911 act which covers the unlawful disclosure of information “prejudicial to the safety or interests of the state”.

It has been used in the past in cases of alleged spying for foreign powers.

It is not believed, at this stage, that either the Russian or Chinese governments were the recipients of the alleged illicit supply of information.

The woman is in custody at a south London police station, while officers are carrying out a search at an address in north London as part of the investigation.

A Met Police statement confirmed she had been contracted to carry out work for a Government department, but did not identify which one, or supply any further details of the suspected offence.

A Government spokeswoman said: "An individual who was contracted to work for the Government was arrested today for an offence contrary to section 1 of the Official Secrets Act, 1911.

"It would not be appropriate to comment further as there is an ongoing police investigation."