Counter terrorism officers stopped a man at Stansted Airport on Sunday night.
He was arrested on Monday on suspicion of terrorism offences and has been taken to a London police station where he remains in custody.
The 21-year-old had returned to the UK from Istanbul, Turkey, via Stuttgart.
Detectives says the arrest was not in response to any immediate threat or risk. Detectives have carried out searches of three addresses in connection with this investigation.
More top news
A film put together by UNISON has highlighted the growing pressures ambulance staff in the East of England are facing.
Outbreaks of rain, heavy at times, tomorrow morning will clear to showers by the afternoon.
Dylan Hartley's World Cup hopes are hanging by a thread after he was hit with another ban. But haven't we been here before?