British counterterrorism police arrested the 41-year-old near Gloucester on November 10. His name has not been made public. Police said the suspicions relate to Russia, but have not identified any information he allegedly obtained or disclosed.

Officers are searching two locations in Gloucestershire. The British investigation was coordinated with the FBI and the US Army, and police said the case is not connected to other ongoing investigations.

What the suspected offences mean

The arrest was made under sections 1 and 3 of the UK’s National Security Act 2023. Section 1 covers obtaining or disclosing protected information; section 3 covers assistance to a foreign intelligence service. The allegations concern suspected offences under those provisions, not a finding that the officer passed information to Russia.

There is also an important distinction between arrest and charge. British authorities had announced no formal criminal charges against the officer. Under the law, he can be held without charge for up to 14 days. His security-clearance level has not been confirmed, and authorities have not said whether any information was actually compromised.

A reported posting at a NATO headquarters

The BBC reported that the officer served at Imjin Barracks in Innsworth, Gloucestershire. The base houses the headquarters of NATO’s Allied Rapid Reaction Corps, a multinational military formation. That reported posting provides context, but authorities have not said that NATO information was involved in the case.

US and British security officials have commented on the case. FBI Director Kash Patel said the case was a matter of utmost concern for the United States and its allies, and said the FBI would not tolerate actions that endangered their security.

What officials have said — and what remains unknown

Vicki Evans, a senior official in the Metropolitan Police’s Counter Terrorism Policing unit, described the arrest as significant, called the allegations serious and said the investigation was continuing. Her comments did not provide details about the information at the centre of the inquiry.

Brigadier General Sean Stinchon, who leads the US Army Counterintelligence Command, said the alleged conduct of a senior soldier entrusted with sensitive information was a sobering reminder that insider threats were real and persistent. He urged people who witness suspicious activity to report it to a local counterintelligence office.

The officer’s identity, the nature of the suspected information and whether it reached anyone remain undisclosed. The investigation is ongoing; the authorities have not announced whether formal charges will follow.