“SCRATCH and sniff “ cards which replicate the smell of growing cannabis are being distributed by the charity Crimestoppers.

The Crimestoppers campaign aims to teach people to recognise the specific smell of growing cannabis in a bid to address the 15 per cent increase in cannabis farms in the UK in 2011/12.

The cards are being distributed by police and Crimestoppers across Yorkshire, including York, North and East Yorkshire.

Lord Ashcroft, founder and chairman of Crimestoppers, said: “Cannabis farms grow more than just drugs.

“Those who are cultivating cannabis tend to be involved in other areas of crime and are often involved in related gang crime and other violent crimes involving firearms.

“These individuals use violence and intimidation to carry out these crimes and endanger the lives of those around them. We want to help put an end to this and the funding that cultivation provides to serious organised crimes like human trafficking and gun crime.”

In Humberside, nearly 300 cannabis farms were discovered by police in the two years from 2010 to 2012.

Areas particularly targeted by the new campaign are West Yorkshire, where 1,800 cannabis farms were found in 2010 to 12, and South Yorkshire, where 1,600 farms were found in the same period.

Over the last two years, police forces have seized more than one million cannabis plants, with an estimated value of more than £200 million.

Often, those behind cannabis farms will illegally hook their factories and properties up to power sources. Energy theft relating to cannabis farming also is estimated to amount to £400 million a year, a spokesman for Crimestoppers said. A recent report has found that commercial or industrial properties are being used less for cannabis cultivation and there has been a significant move by criminals towards residential dwellings.

Andy Bliss, of the Association of Chief Police Officers, said: “We know that many people don’t realise that the empty, rundown house or flat on their street with people coming and going late at night may actually be a commercial cannabis farm.”

Anyone who wants to report a crime anonymously can phone Crimestoppers on 0800 555 111.