The usually calm and well-choreographed royal ceremony known as the “Changing of the Guard” at Buckingham Palace was dramatically interrupted today when a man holding a huge knife to his own throat was tasered by police.

The man, who was dressed in a jacket, jeans and sneakers, broke through a security cordon and held a large knife to his own throat until police moved in and fired at him with the Tasers.

Scotland Yard said the incident happened at 11.55am. The man was arrested and charged with causing affray.

Grant Shepherd, an onlooker at the scene tweeted: "Crazy man with a knife to his throat just stopped the changing of the guard at Buckingham Palace."

Mr Shepherd also took video of the incident which he posted online.

Large crowds had gathered as they often do for the Changing of the Guard ceremony, in which one regiment of guardsmen hand over responsibility for guarding the Queen to another regiment. The handover happens once every two days and is usually accompanied by bandsmen playing music - which can be anythign from military marching tunes to pop songs - as the man appeared brandishing a knife.

Within 10 seconds police arrived on the scene and fired the Taser at the man who, after initially rushing at the police, collapsed.

The Queen and Prince Philip were not in residence at Buckingham Palace at the time of the incident, as they are believed to be in Sandringham.