An intruder who broke into the grounds of Windsor Castle on Christmas Day carrying a crossbow has been sectioned under the Mental Health Act.

On Sunday night a video emerged on social media of a masked man with a crossbow vowing to “assassinate the Queen”.

The video, obtained by The Sun, shows a man in a black hooded jumper wearing a white mask saying: “I’m sorry for what I’ve done and what I will do. I will attempt to assassinate Elizabeth, Queen of the Royal Family.”

The man, who says he is an Indian Sikh, goes on to say that this is “revenge” for those who have died in the 1919 Jallianwala Bagh massacre, as well as those who have been “killed, humiliated and discriminated on [sic]” on account of their race.

The Jallianwala Bagh massacre, also known as the Massacre of Amritsar, took place on April 19, 1919. British troops opened fire on a large crowd of unarmed Indians in the Punjab region of India which was then under British colonial rule, killing hundreds and causing over a thousand casualties.

Scotland Yard on Sunday night confirmed that they are assessing a video following the intruder’s arrest.

The man from Southampton was arrested with the weapon after apparently using a rope ladder to scale a metal fence to enter the gardens at the Queen’s Berkshire residence.

It is understood he was spotted on CCTV “within moments”, triggering a team of armed response officers to arrest him at 8.30am, just hours before the Queen was due to celebrate Christmas with her family.