A man has been detained by armed police outside the Palace of Westminster.
A bearded man, wearing black trousers and a grey sweatshirt, could be seen being held against the fence with his arms behind his back by a police officer.
The incident is not thought to be terror related.
The Carriage Gates entrance to Parliament is closed.
Reports from the scene suggested that armed officers ran from the grounds of parliament and that the man had been tasered.
Scotland Yard said the man - aged in his 30s - was arrested on suspicion of possessing a knife.
There are no reported injuries.
More to follow.