Image caption The card releases a scent that replicates the smell of cannabis when scratched

Marijuana-scented scratch cards are to be posted to thousands of households in a bid to detect illegal cannabis farms.

Crimestoppers, which runs the campaign, said the cards would help people to recognise the smell of cannabis and report suspected plantations to police.

The charity said there was a 15% rise in the number of cannabis farms found in homes between 2011 and 2012.

The West Yorkshire Police area had the largest number of cannabis plantations uncovered in the UK.

According to the Association of Chief Police Officers (ACPO), about 1,800 cannabis farms were found in the area by officers between 2010 and 2012.

Distribution areas by police force Avon & Somerset

Greater Manchester

Hertfordshire

Humberside

Kent

London

Merseyside

Northamptonshire

Nottinghamshire

South Yorkshire

Suffolk

West Midlands

West Yorkshire

South Yorkshire had the second highest number with 1,600 farms uncovered in the same period.

Other hotspots included London, where more than 1,200 farms were detected, Greater Manchester, which had 800 plantations uncovered and Humberside, where officers found nearly 300 cultivations.

'Crackdown on cannabis'

Andy Bliss, from ACPO, said: "Many people don't realise that the empty, run-down house or flat on their street with people coming and going late at night may actually be a commercial cannabis farm.

"It's not just the stereotype of the remote rural set or disused industrial estate unit.

"These farms are often run by organised criminals [and] they bring crime and anti-social behaviour into local communities causing real harm and leaving people feeling unsafe."

Crimestoppers said growers were moving way from commercial and industrial properties and using homes to cultivate the plants.

The green and black cards, which are being distributed to 210,000 households, release a scent when scratched that replicates the smell of cannabis during its growing state.

The charity hopes the campaign would lead to a crackdown on the crime.

Roger Critchell, director of operations at Crimestoppers, said: "We are distributing scratch and sniff cards because not many people know how to recognise the signs of cannabis cultivation happening in their neighbourhood.

"Many are also not familiar with the established links between this crime and serious organised crime."

The initiative started three years ago in Holland, where 30,000 scratch cards were distributed to homes.