Vietnamese-run cannabis farms have in the past year been found at homes in South Wales, Birmingham, East Anglia, Yorkshire, the North East and London

David Brown:

Thousands of cannabis farms are operating from houses after the relaxation of the law banning possession of the drug.

Police are discovering at least three residential cannabis factories a day, according to the drug information charity DrugScope. More than 1,500 have been closed in London alone in the past two years, three times the number found between 2003 and 2005. In 2004 cannabis was declassified, becoming a class C drug.

Domestically produced cannabis now accounts for more than 60 per cent of the drug sold in Britain, compared with 11 per cent a decade ago, research published today says.

Most of the farms are controlled by Vietnamese crime syndicates, which smuggle in illegal immigrants to tend the plants and which rent properties in quiet streets.

Almost every room is used to grow the plants and a home containing 400 plants can yield £500,000 each year.

The gangs bypass electricity meters to power high-intensity lamps and fans without raising suspicion. One cannabis farm found by police had been wired to street lamps. According to the London Fire Brigade, 50 cannabis farms were discovered last year as a result of house fires, caused by faulty lights or rewiring.

Vietnamese-run cannabis farms have in the past year been found at homes in South Wales, Birmingham, East Anglia, Yorkshire and the North East as well as London. Many of the growers, some as young as 15, are made to live in cramped conditions as payback for the gangs that smuggled them in. Police have found growers living in cupboards, to maximise space for plants.

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