More than 7000 farms were detected last year compared with 3000 three years earlier.
Figures released yesterday by Newcastle University suggest as much as £200 million ($400 million) of electricity is stolen every year by growers - many of whom are siphoning power directly from the mains supply to avoid suspiciously high electricity bills.
Jim, a 22-year-old mechanic from Yorkshire, has grown cannabis for the past five years, mainly at a friend's house. He says he makes about £10,000 every four months.
The explosion in cannabis farms has often been portrayed as a relatively harmless cottage industry that allows smokers to steer clear of criminal networks.
But the police have little time for such arguments. They say many of the small plantations are linked to criminal organisations involved in harder drugs, prostitution and trafficking.
British gangs have increasingly moved into the business, which used to be dominated by Southeast Asian gangs. Without the problem of having to elude border controls or high costs of transport, the crops have become attractive to domestic criminals.
A national project has found that of 7000 identified groups of organised criminals, a fifth are involved in cannabis cultivation or trafficking, said Commander Allan Gibson, of the Metropolitan Police. Robberies, burglaries and violence with guns have all increased because of the competition between rival groups.
The Association of Chief Police Officers found that gangs now try to avoid detection by splitting up large growing factories into a number of smaller plants based in homes. A number of "gardeners" are employed to manage smaller-scale operations across a number of sites.
These gardeners typically include criminals forced to work in factories to pay off "debts" to gangs.
Others look to hide the factories in industrial areas so the heavy use of electricity is less likely to be spotted. Daniel Lloyd, a businessman who runs an industrial park in Telford, Shropshire, said police recently raided a unit and discovered a secret farm.
"We had no idea it was there," he said.
"The man told us he needed a place to store gardening equipment and we leased him a unit. When the police raided it we discovered that he had laid out an entire farm with foil sheeting, heat lamps and insulation. Apparently he was shopped by a disgruntled friend."
For amateur horticulturists, the internet has made it easier to grow cannabis successfully. And the success of online seed shops has also made the process easier. Although the cultivation of cannabis is illegal, there is nothing to stop someone buying, selling or importing seeds.
- Independent
