Three men, aged 44, 45 and 48, have been arrested on suspicion of assisting Russia's intelligence service, the Metropolitan Police said.
The men were all arrested by detectives from Counter Terrorism Policing at addresses in west and central London, on Thursday, and are in police custody, the force added. They were detained under section 3 of the National Security Act.
Commander Dominic Murphy, head of Counter Terrorism Policing London, said: "We’re seeing an increasing number of who we would describe as ‘proxies’ being recruited by foreign intelligence services and these arrests are directly related to our ongoing efforts to disrupt this type of activity.
"Anyone who might be contacted by and tempted into carrying out criminal activity on behalf of a foreign state here in the UK should