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.
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The motorist at the wheel of a self-driving car has died after it crashed with a trailer, the first Autopilot death reported in the US.