The NCA said investigators have discovered what they believe to be a sophisticated gun factory on an industrial estate in Hailsham, East Sussex.
Police are continuing to investigate On Saturday evening officers from the NCA’s Armed Operations Unit were deployed to Hailsham as part of a live investigation.
Officers heard loud bangs consistent with gunshots emanating from inside an industrial unit on Diplocks Way.
The unit was an engineering workshop, with signage outside showing it to be a gearbox repair business.
As NCA officers moved in, three men exited the building and they were immediately arrested.
One NCA officer had to discharge a taser to affect the arrest of one of the men.
Two handguns and a quantity of ammunition were recovered.
All three men were later charged with offences relating to the possession of firearms and have now been remanded in custody after appearing before a magistrate.
They were: Kyle Wood, 30, of Gratwicke Drive, Littlehampton; Greg Akehurst, 29, of no fixed address; and 63-year-old Mark Kinman, of Bramwell Mews, Hailsham.
The area around the industrial unit was then cordoned off, and NCA and Sussex Police officers began a thorough forensic search of the site.
That search has taken several days, but officers have found what they suspect to be machinery and components used in the criminal manufacture of firearms and ammunition, including a number of handguns in various stages of production, as well as what appears to be templates and metal for use in their fabrication.
The NCA’s Rob Hickinbottom said: “Our investigation is continuing, and much of what we have discovered at this location will now be the subject of careful forensic analysis. “We suspect that 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 onto the black market and into the hands of criminals. “I would also like to recognise the superb support and assistance we have had from Sussex Police throughout this operation – their contribution to this investigation has been and will continue to be crucial to its success.”