A man was shot with a Taser gun and then arrested by armed police in the grounds of the British Houses of Parliament on Tuesday.
The man, who was wearing a black baseball cap and a green jacket, was pictured surrounded by officers, with one officer pointing his gun towards his head.
Police shouted "Stop. Get down" at the man, before arresting him.
London's Metropolitan Police said the man was arrested on suspicion of trespassing. A Taser was used, police said in a tweet.
The incident is now over, The House of Commons added.
British political journalists, who were in Westminster to cover the latest from an abandoned Brexit vote, were quick to report the news.
Westminster is an area of particularly high security following a series of terror attacks on the British capital's legislature.
In March 2017, Khalid Masood killed four people on nearby Westminster Bridge and stabbed an unarmed police officer to death near Carriage Gates before being shot dead.
In August, a man was arrested after driving a car into pedestrians and cyclists before ramming into barriers outside the parliament building in what police said appeared to be a terror attack.