More than a million cannabis plants have been seized by police over the past two years, with a street value of Â£207m, as organised crime gangs see growing the drug as a â€œlow-risk, highly profitable businessâ€.
The number of cannabis farms detected by police is on the rise.
A new report warns that the commercial cultivation of cannabis poses a â€œsignificant riskâ€ to Britain linked to burglary, violence and the use of guns.
The number of farms detected has more than doubled in recent years to reach almost 8,000, with many now set up in homes or flats rather than factories in order to spread the risk.
More people are also growing their own drugs as a result of the economic downturn, according to the Association of Chief Police Officers study.
The ACPO lead on cannabis cultivation, Met commander Allan Gibson, said: â€œCommercial cannabis cultivation continues to pose a significant risk to the UK. Increasing numbers of organised crime groups are diverting into this area of criminality but we are determined to continue to disrupt such networks and reduce the harm caused by drugs.
â€œThis profile provides a detailed analysis of the current threat from commercial cultivation of cannabis and the work undertaken by law enforcement agencies to combat the threat. It provides a framework to facilitate future planning and decision-making for preventative, legislative and enforcement activity to make the UK a hostile environment for cannabis cultivators.â€
Cannabis has long been the most commonly used illegal drug in Britain, with 6.8 per cent of adults and 17 per cent of young people admitting using it in the past year according to crime surveys.
But whereas in previous decades it was imported in resin form from Africa or Asia, most users now smoke a domestically-grown and stronger herbal type of the drug known as skunk.
When ACPO first started counting the number of farms detected by police forces across the country, in 2007-08, it found 3,032.
Latest figures for 2011-12 show the number now stands at 7,865.
In the past two years a total of 1,096,797 plants were seized with an estimated street value of Â£207m.
Police say there has been an increase in robberies, burglaries and violence linked to the farms, including the â€œtaxingâ€ or stealing of crops and people being kept in â€œdebt bondageâ€ by gang bosses and ordered to cultivate crops.
In order to spread the risk and make it harder for police to spot the farms, which usually use high-powered lights to grow the strong-smelling drugs, gangs are reducing the size of their sites.
Cannabis farmers are managing lots of small farms across residential areas, sometimes even in blocks of flats.
This also allows growers to claim the plants are for personal use if caught, but the report says the number of plants seized is often above 25 which is the threshold for commercial cultivation.
The greatest number of factories were found in west and south Yorkshire, the west midlands, London and the west country.
More than 1m cannabis plants seized in 2 years as police warn of â€˜significant riskâ€™ to UK