Jaswant Singh Chail, 20, who was sectioned under the Mental Health Act 1983 following his arrest, was also charged with possession of an offensive weapon.

Prosecutors confirmed that the decision to press charges followed an investigation by the Metropolitan Police’s counter-terrorism unit.

Mr Chali, who is currently in custody, will appear at Westminster Magistrates Court on 17 August.

He was charged under the Treason Act 1842, which details “Proceedings against Persons guilty of Attempt against the Person of the Sovereign”.

Nick Price, the head of the CPS’s special crime and counter-terrorism division, said: “The CPS has authorised the Metropolitan police to charge Jaswant Singh Chail with offences after he was arrested in the grounds of Windsor Castle on 25 December 2021 carrying a crossbow.

“The CPS reminds all concerned that criminal proceedings against Chail are active and that he has the right to a fair trial.”