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Investigators found a "large-scale" operation in a warehouse in Hailsham, East Sussex, which had described itself as a gearbox repair business. Officers arrested three men found leaving the building and had to use a Taser on one of them, an NCA spokesman said. Gunshots were heard before police raided the building, a spokesman said, possibly as a result of firearms testing in the facility. A NCA officer was injured during the raid but not seriously hurt, a spokesman said. Police said they had already seized 30 firearms, with searches continuing.

The site has been cordoned off while investigations continue. Ammunition was also found at the facility. An NCA spokesman said “components used in the criminal manufacture of firearms and ammunition" like metal, blueprints and templates for guns as well as machinery were discovered. He said: "It is extremely rare to find a gun factory producing using blueprints. "Our investigation is continuing, and much of what we have discovered at this location will now be the subject of careful forensic analysis.

Hailsham gun factory: Police have discovered an illegal gun factory in East Sussex

An illegal gun factory has been discovered in Hailsham, East Sussex

"We suspect this operation has disrupted a group that would appear to be involved in the criminal production of firearms. "As a result, we have prevented a potentially large quantity of weapons from getting on to the black market and into the hands of criminals." NCA photos taken within the gun factory show huge machines and hardware used to manufacture guns. A police spokesman described the factory as "large scale" during a press conference this lunchtime. It is not yet known how long the factory had been operating or if guns had already been supplied and used in other offences.

Ammunition found at the scene of an illegal gun factory in Hailsham