The suspect, in his forties, was detained on Monday under the Official Secrets Act as he tried to leave the UK.
He was taken to a London police station where he is being held on suspicion of spying and sabotage that is “useful to an enemy state”.
The arrest follows a joint investigation by the Met’s SO15 Counter Terrorism Command and MI5.
Police have declined to comment over where the suspect was heading after flying out of Gatwick.
British secret services are on high alert in case of a cyber attack in response to the UK’s support for Ukraine following Russia’s invasion of the country.
The Met said: “We can confirm that officers from the Met’s Counter Terrorism Command arrested a man in his forties at Gatwick airport on Monday 13 June on suspicion of offences under section 1 of the Official Secrets Act 1911.
“He has been taken to a London police station where he currently remains in custody. Enquiries continue.”
