An armed man was arrested after attempting to break into Windsor Castle where the Queen was celebrating Christmas with her family, according to a report in the Guardian newspaper. 

Police said the intruder was carrying an offensive weapon but did not break into any buildings on Christmas Day morning.

A 19-year-old man from Southampton was arrested on suspicion of breach or trespass of a protected site and possession of an offensive weapon, they added.

Officers from Thames Valley and the Metropolitan police responded to a security breach at around 8.30am within the grounds of the castle in Berkshire.

The Sunday Mirror said the arrest came after security controllers monitoring CCTV spotted a man carrying what appeared to be a crossbow.

The Mail on Sunday said sources suggested the man was armed with a crossbow and used a rope ladder to scale a metal fence.

Police did not confirm what the weapon was and it is not known where exactly the man was on the grounds and how close he got to the castle itself.

The Queen was celebrating Christmas at Windsor with Prince Charles and his wife, Camilla, in the first year since the death of her husband, the Duke of Edinburgh.

Members of the royal family have been informed about the incident.