The crossbow intruder at Windsor Castle, named as 19-year-old Jaswant Singh Chail, has been “sectioned under the Mental Health Act” and “following the man’s arrest, detectives are assessing the contents of a video”, Scotland Yard has said.

The video appeared to be one made public by The Sun tabloid, in which the alleged intruder appears to hold a “shiny black weapon” and wears a “sinister white mask”.

The Sun has deciphered his words although his voice is said to be distorted: “I’m sorry. I’m sorry for what I’ve done and what I will do. I will attempt to assassinate Elizabeth, Queen of the Royal Family.

“This is revenge for those who have died in the 1919 Jallianwala Bagh massacre.

“It is also revenge for those who have been killed, humiliated and discriminated on because of their race.

“I’m an Indian Sikh, a Sith. My name was Jaswant Singh Chail, my name is Darth Jones.”

The newspaper points out that “in Star Wars, the Sith are the enemies of the Jedi Knights and worship the dark side of ‘the Force’.”

The Sun added that the pre-recorded video was posted at 8.06am on Christmas Day, 24 minutes before a youth was captured inside the grounds of Windsor Castle, some 500 metres from the Queen’s private apartments.

The Queen had her Christmas lunch this year at Windsor, where she was joined by Prince Charles and his wife, Camilla, and other relatives.

Alongside the video, a message was also sent on Snapchat that said: “I’m sorry to all of those who I have wronged or lied to. If you have received this then my death is near. Please share this with whoever and if possible get it to the news if they’re interested.”

The Daily Mail has managed to speak to the youth’s 57-year-old father, Jasbir Singh Chail, at the family’s £500,000 home on a private estate in North Baddesley, Southampton.

Chail senior, who is listed as the director of an IT company along with his 51-year-old wife, is described by the Mail as “well spoken”.

He said: “Something’s gone horribly wrong with our son and we are trying to figure out what. We’ve not had a chance to speak to him but are trying to get him the help he needs. From our perspective, we are going through a difficult time.”

According to the Mail, Jaswant, known to friends as “Jas”, “is believed to have enjoyed a comfortable, loving upbringing surrounded by his family in the middle-class district where they live”.

Neighbours reported hectic police activity at the Chail home.

One neighbour said: “There was a big commotion with all the police around and it caused some concern, especially as it was Christmas Day. The family keep themselves to themselves, like the rest of the estate, but we know there’s a teenage lad who lives there with his mum and dad. The police didn’t leave the estate until late at night. We saw the Windsor story in the news but never thought our road would be at the centre of it.”

There has long been a campaign to persuade the British government to offer a full apology for the Jallianwala massacre.

The Labour MP for Ealing Southall, Virendra Sharma, told The Telegraph: “For many years, I have called for a formal British apology for the Jallianwala Bagh Massacre, a campaign that thousands have supported since 1919. The matter continues to be significant, and as events in recent days have shown deeply important to millions of British-Indians living in the UK. However, the threat or impression of a willingness to commit acts of violence today to secure an apology is totally wrong, it undermines the campaign, rather than strengthens it.”