A 57-year-old British national—identified by authorities only as David S—was detained on Tuesday following a joint investigation by British and German authorities.
The German Federal Prosecutor’s Office said the man is suspected of selling documents obtained during the course of his work to “a representative of a Russian intelligence service.”
A UK government spokesman said the suspect had been “contracted to work for the government,” but British officials would not comment on reports that the suspect was working as a security guard at the embassy.
The situation has prompted security concerns from MPs.
Labour MP Chris Bryant, the chairman of the all-party parliamentary Russia group, told The Daily Telegraph the British government “must review the security of all contractors at UK embassies as a matter of urgency.”
He described the arrest as potentially “one of the most serious security breaches at a UK embassy for many years.”
The Telegraph reported Conservative MP Tobias Ellwood, chairman of the Commons Defence Select Committee, has also called on the government to review the security of all contractors working at UK embassies, which he described as “standard protocol following such an incident,” adding the incident is a “disturbing throwback to the Cold War days.”
The man identified as David S—who was arrested in the city of Potsdam, to the southwest of Berlin—is being held under German law on suspicion of engaging in “intelligence agent activity.”
The Metropolitan Police said officers from the force’s Counter Terrorism Command—which investigates alleged breaches of the Official Secrets Act—are liaising with their German counterparts who have “primacy” for the investigation.
Following the man’s detention, searches were carried out at his home and at his workplace.
The German Foreign Ministry said it is taking the case “very seriously.”
Foreign Minister Heiko Maas told reporters: “Spying on a close ally on German soil is absolutely unacceptable and we are in full solidarity with our British friends.
“We will be following the federal prosecutors’ further investigations very closely. And where that’s desired, necessary, and possible, we will also support them.”
German prosecutors said the man had been working as a “local employee” at the embassy.
In a statement, the Metropolitan Police said: “The man was arrested in the Berlin area on suspicion of committing offences relating to being engaged in ‘intelligence agent activity’ (under German law).
“Primacy for the investigation remains with German authorities. Officers from the Counter Terrorism Command continue to liaise with German counterparts as the investigation continues.”
A UK government spokesman said: “An individual who was contracted to work for the government was arrested yesterday by the German authorities.
“It would not be appropriate to comment further as there is an ongoing police investigation.”
The arrest comes at a time of continuing tensions between the UK and Russia, which have been building for a number of years.
In June, a Royal Navy warship was buzzed by Russian fighter jets when it sailed through disputed waters off Crimea which was annexed by Moscow from Ukraine.
In 2018, Britain expelled 23 Russian intelligence officers following the poisoning attack on former spy Sergei Skripal in Salisbury, which persuaded allies to eject dozens of others.
By Ben Hatton and Gavin Cordon