In some ways, it is a rare British success story. A home-grown product develops such a global reputation it is exported around the world despite fierce international competition.

Last week's report by the Association of Chief Police Officers that so much cannabis is being produced in Britain the drug is being distributed abroad shocked most commentators.

But the findings that Britain's huge, secretive complex of cannabis "factories" – many rented houses – are looking to export came as no surprise to those who monitor organised crime in the UK. They have known for some time that "growing your own" is no longer the preserve of hobbyists and hippies with access to a greenhouse.

Britain's opportunist underworld has been quick to spot an emerging market in skunk, the most potent strain of cannabis. Profit margins are enticing. A factory can cost £20,000 to establish, an outlay that can be recouped by an initial harvest within two months. In a year, a single factory can yield up to £500,000. International policing operations have disrupted traditional smuggling routes from countries like Morocco, a historical supplier of cannabis resin to the UK.

The popularity of skunk above resin partly explains the sudden explosion in growth of Britain's cannabis factories. Strong skunk varieties carry a cachet and a number of cannabis users have focused their business strategy on increasing the strength of their plants.

Seeds are carefully cultivated to produce plants of steadily higher potency. For years, the Netherlands held the reputation for producing some of the strongest skunk around. Users claim that newer UK varieties have started to rival Dutch produce. The word went out: buy British. Thousands of factories have sprung up in the past few years. Officers closed down nearly 7,000 in the last year. Growers have taken advantage of the recession by turning abandoned factories, clubs and banks into factories.

The first step to large-scale production is creating the optimum climatic conditions that mimic the hot, humid temperatures that foster rapid cannabis growth. Properties are relatively simple to convert into plantations. Hydroponic equipment, easily bought over the internet or legally from garden centres, creates the nutrient delivery and automatic irrigation systems required for rapid growth. The one pitfall for the large-scale cultivator is heat.

Hundreds of factories have been uncovered by the sustained temperatures needed to produce the crop. Neighbours have noticed that during heavy snowfalls, roofs have remained warm enough to melt the snow. In other cases, wallpaper has peeled off in adjoining terraced houses. Officers use thermal-imaging cameras to identify production centres.

The growth of the cannabis factory was initially orchestrated by Vietnamese gangs in districts like Hackney, east London. However, intelligence identifies a growing number of white Britons muscling in.

British involvement has grown in tandem with the market. As recently as 2005, just 15% of Britain's cannabis was home grown; by 2008, it was 90%, with the latest phase pointing to export.

In factory terms, 800 were uncovered in 2006, spiralling to more than 6,800 in 2009-10. Police believe every small British town may have its own cannabis factory. In West Yorkshire, for example, officers found 896 factories last year. As with all criminal enterprises, evidence suggests the landscape is already evolving. Recent discoveries indicate more sophisticated forms of insulation to avoid detection. Factories are more likely to be booby-trapped. The increased role of organised crime means weapons are being found.

So far, the biggest cannabis factory uncovered by police contained more than 7,600 plants with an estimated value of £2.5m. History may shortly judge the Cambridgeshire factory's production to have been modest.