The terror-related arrest of a teenager at Heathrow airport was not made in response to any immediate risk or threat, police said.
A 19-year old man has been arrested on suspicion of "preparing for acts of terrorism" in relation to Syria.
The man is currently held at a police station in London.
More top news
Medical staff who helped during the Westminster terror attack have received a royal thanks for their life-saving efforts.
Colin Gregg, the son of the founder of the Greggs bakers chain, has been jailed at Newcastle Crown Court for 13 and a half years.
Khalid Masood was killed by a single gunshot to his chest, after the terror attack which claimed the lives of four people, an inquest heard.