Police on the scent of cannabis farms are delivering ‘scratch and sniff’ cards to 10,000 homes across Greater Manchester alerting residents to the tell-tale aroma of cultivation.

The A5-sized cards, part of a national campaign being launched today, emit the smell of cannabis as it is growing... although they do not contain any active element of the plant.

The leaflets warn unsuspecting residents to look out for high-tech equipment, covered or blocked windows, constant lighting and buzzing ventilation on their street.

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They also warn about any excessive cables trailing from the street and late-night visitors. All could indicate that a house is being used to grow cannabis - alongside the sickly sweet smell the cards reveal.

GMP seized a staggering 51,000 plants last year, according to Home Office data, and in 2011/12, 89,000 cannabis plants were seized – higher than anywhere else in the country.

Police figures show there have been 397 arrests for the commercial cultivation of cannabis in Greater Manchester so far this year.

Energy regulator Ofgem says a third of energy theft is linked to cannabis farms.

Det Supt Mark Smith said cannabis worth £80,000 could be grown in an average terrace house in three months.

He said: “Organised criminals see cannabis cultivation as a low risk, high profit venture and there is clear evidence that they use cannabis production as a way to fund a range of other criminal activities, such as violent crime, people trafficking and prostitution.

“To produce the cannabis criminals often rent properties such as flats or suburban houses and as a result may bring violent crime into law-abiding communities.

“I would urge everyone to act as our eyes, ears - and noses - to sniff out these criminals.”

Crimestoppers hailed the success of last year’s scheme, which nationally led to a 28 per cent rise in intelligence, 400 more arrests and cannabis seizures worth £2m in London alone.

This year 17 ‘hot-spot’ areas, including Greater Manchester, are being targeted.

Crimestoppers’ northern manager Dave Hunter said criminals use cannabis to fund further crime.

He said: “We’re not looking to target individual users, we’re looking at something much bigger.”