Ventilation and lighting systems using stolen electricity bypassed through high voltage transformers were being employed to cultivate 100 plants in the loft at 152 Winsover Road.

And the three first floor bedrooms housed hundreds more pots containing cannabis plants already harvested.

No-one was in when officers forced the door at 9am on Tuesday and the hunt for suspects was continuing yesterday.

Police were alerted by members of the public who reported unusual lighting in the upper rooms at night.

Occupant may have been forced to live in house.

Though one downstairs room was being used as a store for compost, fertiliser and growing equipment, at least one person had been using the kitchen shortly before the raid and there were makeshift beds downstairs.

Det Sgt Gregory Ing said: "Officers found a highly sophisticated hydroponic cannabis cultivation operation. The first floor and loft of the house had been converted with the purpose of producing large quantities of the drug.

"The walls had been covered with reflective sheeting. An extensive lighting system, which bypassed mains electricity, had been set up and a ventilation system running through the whole house had been put in.

"This operation is clearly the work of organised criminals. This is a fantastic result in the sense that the operation has been shut down and the drugs will not hit the streets.

"Thousands of pounds worth of drugs have been recovered and a criminal outfit that was capable of turning out tens of thousands of pounds worth of cannabis every year is out of business."

Police are appealing for anyone with information on those living at the address to call Spalding Police Station on 01775 722233 or Crime-stoppers anonymously on 0800 555111.