A terrorism investigation has begun in London after an assailant stabbed a policeman outside the Parliament building.
The alleged assailant was shot by police at the scene and several people have died or been seriously injured.
The man appears to have deliberately driven a vehicle into several people walking on the nearby Westminster Bridge.
Our Correspondent Catherine Drew is at the scene.
She says the police are questioning tourists at nearby "London Eye", a giant Ferris wheel...
IN: Tourists, including...
OUT: ...London.
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