More than £1 million worth of cannabis plants have been seized after the police received a tip off from a member of the public.
Avon and Somerset Police discovered around 1,000 plants at an industrial unit in Kingswood, South Gloucestershire.
Electricity had been diverted from a nearby substation to power the equipment used to help grow the plants.
A spokesperson for the force has described those behind the operation as 'organised criminals' who were 'exploiting vulnerable people'.
"Those responsible for producing these plants were not doing it as a hobby or for their own personal use, they are organised criminals who we believe were exploiting vulnerable people to unscrupulously line their pockets.
Officers are now urging people to keep coming forward with information after their successful raid, which was a result of a public tip-off.
"Please keep coming to us with information, it really does make a difference to disrupting organised crime, safeguarding vulnerable people often trafficked or kept as slaves and to preventing the sale of illegal drugs in our communities."
They are reassuring people that information can be disclosed anonymously.
"No personal details are taken, information cannot be traced or recorded and you will not go to court or have to speak to police when contacting Crimestoppers."