A man arrested with a crossbow at Queen Elizabeth's Windsor Castle home outside London on Christmas Day last year said "I am here to kill the Queen", a British court was told on Wednesday.

Jaswant Singh Chail, 20, who has been charged under Britain's Treason Act, appeared in the grounds of Windsor Castle wearing a hood and a mask, the court was told. A police officer said he looked like someone from a vigilante movie.

The queen was at the castle at the time of the incident on December 25, along with her son and heir Prince Charles, his wife Camilla and other close family.

Following an investigation by counter-terrorism police, Chail was charged with making threats to kill, possession of an offensive weapon and an offence under section 2 of the Treason Act 1842.

This section details punishment for "discharging or aiming fire-arms, or throwing or using any offensive matter or weapon, with intent to injure or alarm her Majesty".

A hearing at London's Westminster Magistrates' Court was told Chail, from Southampton in southern England, said he wanted revenge on the establishment.

Cover photo: The entrance of the Westminster Magistrates' Court, in London, prior to the start of the hearing of Jaswant Singh Chail. Carlos Jasso / AFP