A 21-year-old man has been arrested at Stansted Airport on suspicion of terrorism offences.
Scotland Yard said he was suspected of being involved in the commission, preparation and instigation of terrorism but his arrest was not in response to any immediate threat or risk.
The Met Police told the BBC that Counter Terrorism Command officers detained the man on his return to the UK from Istanbul, Turkey, via Stuttgart in Germany.
He was stopped on Sunday evening and arrested four-and-a-half hours later.
Police said the man remained in custody at a London police station and inquiries are ongoing.
