And the entire firearms unit was given a dressing down after a bullet from a police rifle was lost at the scene and was later found by a member of the public.
Procedures have been reviewed and tightened as a result of the embarrassing and potentially dangerous mistake.
The order to disarm came from the top when intelligence suggested that the man at the centre of the siege on 13 July – 30-year-old Lee Albert de Mouilpied – was only armed with an air rifle.
Deputy police chief Lenny Harper is believed to have given the order to the firearms unit to disarm, as he was ‘gold commander’ in charge of the police operation on the day.
He did not want the man to be shot by police while he was in possession of a non-deadly weapon, even if he directly threatened to shoot officers with it.
The JEP understands that there was dissent among some of the officers, who believed that an air rifle was still a potentially dangerous, even potentially fatal, weapon and that they should still have the right to shoot him if they thought it necessary.
A small number are believed to have threatened to walk off the firearms squad in protest at the decision.