The cards are part of a Crimestoppers campaign, launched today, to curb the growing problem of cannabis factories in the UK, which have increased by 15% over the 2011/12 financial year.

Crimestoppers commissioned the cards so that members of the public would be aware of the smell of growing cannabis in their local areas and inform the authorities.

The campaign was inspired by a successful earlier project in Holland, which was the brainchild of advertising and marketing agency The Edge Factory.

But finding a chemical company capable of distilling cannabis oil, removing the psychoactive element Tetrahydrocannabinol (THC) and putting it into microcapsules and a printer which could put it into microcapsules and print them onto card was not easy.

Managing director JanCees Neef said: "We put a lot of research into this, we tested it with screen printing and offset. It took three years to get to production."

Neef finally found an American-based multinational printer with the sponge-based printing technology needed. The company, which Neef refused to name, has this facility in Poland and France.

Founder and Chairman of Crimestoppers, Lord Ashcroft said: "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. We want to help put an end to this."

The cards are being delivered to addresses across the UK this week. Crimestoppers is asking anyone with information to call 0800 555 111 anonymously or visit www.crimestoppers-uk.org.