Police last night hailed a key victory in the battle against drugs production in Norfolk after uncovering a huge cannabis factory in a disused former MoT testing station.

Police last night hailed a key victory in the battle against drugs production in Norfolk after uncovering a huge cannabis factory in a disused former MoT testing station.

Officers estimate cannabis worth up to £400,000 a year could have been produced in the sophisticated operation in the anonymous-looking brick unit on the Threxton Road Industrial Estate at Watton.

Good old-fashioned policing was at the heart of uncovering the factory late on Saturday night as two officers patrolling the estate stopped a car which had been parked outside.

Three people from the Yarmouth area were inside the vehicle and officers found buckets full of cannabis in the back and a set of keys which fitted the lock to the unit.

The discovery is the latest in a series of drugs factories which have been found in Norfolk at homes and in industrial units, including in Norwich, Lyng near Dereham, Yarmouth, King's Lynn, Terrington St Clement, Thetford and Attleborough.

Describing the discovery in Watton, Sgt Colin Barratt, of Dereham police, said: “This is a major operation and we are looking at big- scale production by people who are very well organised and professional. It is a major find for the area in terms of potential harm it could do and it is a major disruption for the drugs industry.”

He praised the officers who made the discovery.

“It was good pro-active policing.”

Inside the building - which appeared empty and is right in a quiet corner of the estate - the officers found 591 cannabis plants in one part of the building which had been growing under an intricate system of lighting.

Extensive work had been done inside the building to create insulation to help the plants grow and prevent anything being seen or heard from outside.

It appeared a second large room was being set up to grow hundreds more cannabis plants - and there was also evidence that it was possibly being used for storage of equipment for further factories.

It is believed the cannabis plants were growing on a 13-week cycle with each one potentially being worth £100,000.

Police allowed the Times into the factory to show the true extent of the operation which was going on and it is a significant blow to the criminals who use secluded areas of Norfolk to grow drugs.

Earlier this year, a man was jailed for two years and four months after admitting cultivating cannabis in Norwich.

Yesterday, scenes of crime officers carried out detailed examinations at the Watton factory and inquiries are continuing into how the factory could have been set up.

Workers from energy company EDF went to isolate the electricity supply, which had bypassed the meter system to prevent suspicion.

There were 65 lights, each with 600-watt bulbs and the lights were on a 12hr-on/12hr-off system to ensure the best growing conditions for the plants.

Last night, the three men were in custody on suspicion of possessing cannabis with intent to supply and cultivation of cannabis.