Cannabis 'scratch and sniff' cards handed out by police across England and Wales

Cards loaded with smell of cannabis have been handed out by 17 police forces to help residents identify the smell of illegal farms

It is not known whether or how cannabis has a direct effect on sperm production (Getty Images)

People are being taught to recognise the smell of cannabis using ‘scratch and sniff’ cards handed out by 17 police forces across the UK.

Police say the cards are being used to educate the public on what cannabis plants smell like, so they can alert authorities to the presence of illegal farms in their local area.

Cards were handed out by forces including Greater Manchester Police and Hampshire Constabulary as part of the second phase of a publicity drive targeting cannabis hotspots, launched last spring.

The scheme follows a similar project in the Netherlands that saw a pilot cannabis scheme rolled out across the country to help residents detect if their neighbours are operating illegal plantations.

The National Police Lead for Cannabis, Chief Superintendent Bill Jephson, said: "Those who commercially cultivate cannabis are serious and organised criminals often involved in other criminal ventures.

“Houses in residential areas are used to produce the cannabis, which brings violent offenders into the heart of our communities and leads to a real risk of fire and flood."

Figures from the UK Human Trafficking Centre found that in 2012 around a fifth of human trafficking victims thought to have been criminally exploited were forced to get involved in growing cannabis. Eighty-one per cent of these were children.

Detective Superintendent Kath Barnes, from Hampshire Police, said: "Cannabis is often seen as harmless and somehow acceptable. This is just not the case.

“It's harmful to use and many people including children, across the world, are exploited in furtherance of the cannabis trade."

The Founder and Chairman of Crimestoppers, Lord Ashcroft KCMG PC, said: "The campaign run by Crimestoppers last year highlighted just how much people care about removing cannabis farms from their community.

"Quite often, those running cannabis cultivation operations are also involved in other serious and organised crime, such as human trafficking and possession of weapons."

Additional reporting by PA