The suspect, in his 40s, was detained by the Metropolitan Police at Gatwick Airport in West Sussex on Monday evening.
A Scotland Yard spokesman said: “We can confirm that officers from the Met’s Counter Terrorism Command arrested a man in his 40s at Gatwick Airport on Monday 13 June on suspicion of offences under Section One of the Official Secrets Act 1911.
“He has been taken to a London police station, where he currently remains in police custody.
Section One of the Act relates to information contained within notes, plans or sketches which may be “useful to an enemy state”.
The man was set to catch an outbound flight when he was arrested.
A source told the Sun: “The suspect is believed to have been in the UK spying on behalf of the Putin regime.
“He was kept under observation and arrested as he arrived at Gatwick to try and fly out of the country.’’
He was taken to Hammersmith police station, West London.
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