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.
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.