detectives were greeted by amazing scenes when they raided homes in the region as part of a drugs operation.

From the outside, the houses appeared to be normal homes, but inside they had been converted into mini- cannabis factories.

Their existence was kept so secretive that even neighbours in the small close-knit communities had no idea about what was happening.

Last week, warrants were issued for eight houses in the South Durham area where police uncovered 1,500 cannabis plants, which had the potential street value of £1.5m.

Detective Inspector Billy Hugill, who is leading the investigation, said the operation codenamed Applejack had taken huge steps towards breaking up what appears to be a major organised crime ring.

He said: "This is organised crime at its highest. We were surprised at the scale of it and how elaborate the operation was.

"The houses have been altered solely for the purpose of growing cannabis.''

It appears that drug dealers are cashing in on the region's lower property prices by buying or renting houses to set up the enterprises.

Operation Applejack started last weekend when detectives raided a house in Murphy Crescent, Bishop Auckland, recovering in excess of 300 cannabis plants.

Later the same day, more than 400 plants were seized from a house in Collingwood Street, Coundon.

The raids carried on across South Durham, with 370 mainly mature plants seized in Haig Street, Ferryhill, and more than 500 taken from High Street, West Cornforth.

A house in Eden Close, Coundon, was also targeted. No cannabis plants were found, but equipment used in the cultivation of the drug was discovered.

So far, six men and one woman, aged between 25 and 46, have been arrested.

Three men have appeared before South Durham magistrates, in Newton Aycliffe, and have been remanded in custody. Two of those men are due to appear at the court again today.

Det Insp Hugill said he could not rule out the possibility of more raids.

He said: "There may be more arrests to come. The investigation is still ongoing and it is taking us outside of the region."