According to the Daily Mail, the development has infuriated detectives seeking to break the stranglehold of Vietnamese barons, who control 75 per cent of UK production of cannabis.
Senior police sources confirmed there has been an "explosion" in Vietnamese-run cannabis factories over the past year. Sometimes the gangs rent up to four properties in a row from the same landlord. Each house can produce up to four harvests a year, worth up to 600,000 pounds.
Electricity connections are often tampered with to offer a free supply to power the lighting around the plants.
Following a recent crackdown by Scotland Yard, many of the crime syndicates have relocated out of the capital to rented properties in places such as Birmingham, Sheffield, Manchester, Nottingham, Leicester and Derby.
According to investigators, the Vietnamese gangs have a distinct four-tier structure. There is usually a financial backer, who owns a UK business such as a nail bar or restaurant. There is a "consultant" who travels around the country advising people how to set up a cannabis farm. Then there is the "gardener", and finally a seller, responsible for distribution of the drug.
The groups typically launder their vast profits in businesses, vehicles and property. Links to casinos have been uncovered in the Midlands.
Senior officers believe privately that the Government's decision to relax the laws on cannabis is the cause of the surge in home-grown production.
Chief Superintendent Jon House, of South Yorkshire Police, said the downgrading of the drug from Class B to Class C should be reversed.