A man who was Tasered at the gates of Parliament on Tuesday has been arrested under the Mental Health Act.

Witnesses heard a scream and then shouting as police ran towards the man inside Carriage Gates in the shadow of Big Ben, just yards from where Pc Keith Palmer was stabbed to death last year.

The man, described as dark skinned and wearing an olive-coloured shirt, was immediately detained by uniformed officers.

He was Tasered and struck with a baton by officers inside the precincts and then pinned to the ground just yards inside the gates.

One report said the man had gained access to the Parliamentary estate. He was handcuffed and bundled into a police van, and driven away.

A spokesman for the Metropolitan Police said: "A man was arrested by Carriage Gates, inside the Palace of Westminster, on suspicion of trespassing on a protected site at around 11.55hrs on Tuesday, 11 December.

"A Taser was deployed. Enquiries into the circumstances continue."