A man is reported to have been arrested at Stansted on suspicion of terrorism offences.
The 21-year-old was suspected of being involved in the commission, preparation and instigation of terrorism, according to Scotland Yard.
Counter Terrorism Command officers detained the man on his return to the UK from Istanbul via Stuttgart, Met Police said.
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 where he had been taken following the arrest, the BBC reported.
“This arrest was not in response to any immediate threat or risk,” a Met spokesperson added.
“Detectives have carried out searches of three addresses in connection with this investigation.
“Inquiries are ongoing and we are not able to give further detail at present.”
A spokesman was unable to confirm whether the arrested man was suspected of travelling to Syria.