He was armed with a powerful crossbow with the safety catch off that was capable of firing bolts with "lethal" effect, the Old Bailey was told.

The officers discovered that Mr. Chail was carrying a crossbow, loaded with a bolt with the safety catch off.

“Thumb on the safety catch as you walk, so you can release immediately if something happens!”

Prosecutors allege the former supermarket worker from Southampton in southern England was wearing a hood and a mask and carrying a loaded crossbow with the safety catch off.

This included the guard "handover drill" and checking the safety catch of the machine gun, the lawyer said.