A HUGE and “highly-sophisticated” cannabis factory at a disused industrial unit was discovered by police attending what they thought was a burglary.

Officers responded to an emergency call from a security guard at a nearby unit on Cheney Manor Industrial Estate late on Thursday but when they arrived they found the site packed with more than 1,000 cannabis plants – which have an estimated street value of more than £500,000.

It is one of the biggest cannabis seizures in the town’s recent times, second only behind a raid at Poplar Farm, Wanborough to smash a £25m drugs ring smuggling the class B substance in with fresh flowers.

Detectives have said they are unable to tell how long the factory had been running but that it would have taken a long time to put together, with lighting rigged in seven rooms packed full of plants at various stages of growth.

Although no-one was at the scene when police arrived there was evidence of rudimentary living quarters, comprised of just a mattress on the floor.

Police are appealing for witnesses and Detective Sergeant Joe Saunders said: “This was a sophisticated set-up and it will take a lot of time to analyse and investigate. It is certainly one of the biggest in recent history.

“We had a report of a burglary from a member of the public close by but when officers arrived they found the premises like this.

“There are three rooms in the basement and several rooms on the ground floor full of cannabis plants.

“They are at different stages of growth and it indicates there was an organised production line – factory certainly is an apt description.

“An operation like this would have taken a lot of time setting up and it will take some time to go through it, collect evidence and make enquiries through the landlord and CCTV.

“We are pleased that we, along with the member of the public who phoned us, have stopped a huge amount of cannabis making it on to the streets of Swindon.

“This is not just a little bit of weed – the people behind this were making a lot of money from the sale of illegal drugs.

“We are very mindful of the location and will be looking at any intelligence we have, while keeping an open mind about who is behind it.

“We would like to hear from anybody who knows anything that could help our enquiry.”

The unit lies in between Flextronics and Anything Stone, neither of whom are associated with the incident, and has been cordoned off by police as forensic teams worked to secure evidence.

Anyone with any information should contact DC Yvonne Ridge on 101 or Crimestoppers anonymously on 0800 555 111.