Cannabis is a growing problem for landlords as crime gangs change tactics to hide their stashes in buy to let homes to avoid police.
Police forces all over the country have raided rental properties with sophisticated lights and watering equipment need for growing the drug.
Many of the cases are linked to Asian drugs gangs that are spreading the risk of detection by setting up farms in suburban rental properties rather than larger commercial concerns.
Typically, the properties house 200-300 plants tended by one or two illegal immigrants, usually from Vietnam.
In the most recent case, Wolverhampton Crown Court heard how a landlord let a home to illegal immigrant Mo Nguyen, 22, acted as a grower for the drugs gang.
Nguyen was jailed for two years after pleading guilty to producing cannabis. He faces deportation at the end of his prison term.
The farm was discovered when the landlord was called to the house to investigate a humming noise. Inside, he found 340...
cannabis plants worth around £100,000 and growing equipment making the noise.
Nguyen claimed he was working off a £10,000 debt owed to the gang for bringing him to the UK.
Another Vietnamese illegal immigrant Vinh Cong Le, 18, was given 20 months detention by a judge at Peterborough Crown Court for producing cannabis worth £130,000 found by police who raided a four-bedroomed buy to let home in the city.
His lawyers are appealing his conviction on the grounds he was a victim of human trafficking.
They told judges at the Court of Appeal, London, that a drugs gang forced him to tend their crop to pay back costs of smuggling him in to the UK. They claim his conviction should be quashed as European Law forbids victims of trafficking from being charged with a criminal offence.
The UK Border Agency told the court no evidence showed he was a victim rather than a member of the gang.