Page last updated at 00:20 GMT, Tuesday, 3 November 2009
'Hash in the attic'

cannabis farm
Skunk, the type of cannabis grown in farms, is up to three times more potent than other varieties because it contains higher levels of the active ingredient THC

How much does it cost to set up a farm?

Police estimate that it costs about £15,000 to establish a large-scale cannabis farm. That includes the cost of renting a premises and getting equipment such as lights and ventilation in place. Some gardeners illegally divert the electricity supply, normally from a separate supply taken from the main incoming supply. This carries an inherent safety risk, due to the amount of electricity being taken without proper protection at the installation. On average, £17,000 of damage is caused to each property converted into a farm.

What type of cannabis is produced in farms?

Skunk is grown in farms. It is up to three times stronger than other types of cannabis because it contains higher levels of the active ingredient - tetrahydrocannabinol (THC). It is called skunk because of its strong smell. The UK government said it reclassified cannabis from Class C to B to reflect the fact that skunk now dominates the UK market. Some scientists have concluded that this variety gives users a higher risk of mental health problems. Skunk now accounts for about three-quarters of police cannabis seizures, compared to 15% in 2003.

How much money can be generated from cannabis farms?

The Independent Drug Monitoring Unit's research has suggested that at the smallest level, three or four plants could produce £200-£300 worth of cannabis. A one-room conversion may yield about £10,000-£15,000 annually. When an entire property is turned over to growing cannabis, about £60,000-£70,000 worth of the drug could be produced in a year. On the largest, industrial scale, crops worth up to £400,000 a year could be harvested.

What are the telltale signs of the existence of cannabis factories in residential properties?

Windows are permanently covered from the inside because of condensation. The cannabis or by-products such as used fertiliser may be removed in black bin bags or laundry bags. There could be a vent protruding through the roof or a rear window and the sound of fans may be audible.

What are the penalties for people involved in cannabis factories?

The Home Office website lists the maximum penalty for supply, dealing, production and trafficking of cannabis as 14 years imprisonment. People caught in possession of the drug can face a maximum of five years in jail.

[Sources: Police, the Home Office and the Independent Drug Monitoring Unit]

Hash in the Attic will be broadcast on Tuesday, 3 November on BBC One Scotland at 2235 GMT.

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