The Federal Security Service (FSB) announced the detention and said a criminal case had been opened under Article 275 of the Russian Criminal Code, which covers state treason.
According to the FSB, the detained man collected information about British Embassy staff, including their addresses and details of their meetings and travel. The security service also alleges he studied data on the diplomatic mission's security system and on events held there.
The FSB said the man acted in the interests of Ukraine's Security Service. He allegedly received his assignments from Ukrainian blogger Dmitry Karpenko, known under the pseudonym Apostol. Karpenko is the founder of the "Look for Your Own" project, which helps identify killed and captured Russian servicemen.
According to the FSB, Kyiv planned to use the gathered information for attacks on British Ambassador Nigel Casey and other diplomats. Responsibility for those attacks was allegedly to be pinned on Moscow, in order to draw London into a direct conflict with Russia, secure an increase in arms supplies to Ukraine and tighten sanctions.
The day before, London's Metropolitan Police reported the arrest of a 31-year-old British resident, Joshua Cammidge. He is accused of violating the National Security Act. According to the counter-terrorism unit conducting the investigation, Cammidge was in contact with a representative of the "GRU Volunteer Corps," a group the investigation says is controlled by Russian intelligence.
Accounts differ: the FSB calls the detained man a current embassy security employee, while TV Rain reports he is a former guard. The agency's statements also differ on the list of targets, ranging from the collection of data on diplomats to the preparation of attacks against the ambassador; the latter is presented as the security service's version.