British police have arrested three people suspected of assisting a foreign intelligence service, saying the investigation related to Russia, the latest allegation of spying activities on behalf of Moscow in Britain.

The three, two men, aged 41 and 46, and a 35-year-old woman, were arrested in Essex, east of London, accused of offences under the National Security Act, which was brought in two years ago to give new powers to target threats from foreign states.

"Through our recent national security casework, we're seeing an increasing number of who we would describe as 'proxies' being recruited by foreign intelligence services," said Commander Dominic Murphy, head of London police's Counter Terrorism Command.

London has repeatedly accused Russia or its agents of being behind spy plots and

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