A new report estimates that 500,000 people grow cannabis in the UK – roughly one person on every street. So how can you tell if your neighbour is raising a crop?

In the course of making a film about Britain's cannabis industry, I have learned a lot about how to spot a cannabis farm. I have been schooled by policemen who raid them, gangsters who rob them and growers who set them up and produce more than 80% of the cannabis smoked in the UK today.

The latest Independent Drug Monitoring Unit report suggests there are now as many as half a million people growing cannabis in the UK, which equates to roughly one on every street. So how can you spot the cannabis farm next door to you?

Smell Follow your nose. A cannabis crop takes about three months to produce. During the final four weeks, the plants stink. Earlier this year, Crimestoppers helpfully issued cannabis-farm scratch-and-sniff cards to 210,000 homes in the UK to help you identify the exact bouquet.

Light Growers can't get away from the fact that internal farming requires a lot of it: 2,000 watts running 12 hours a day in a small bedroom looks a lot like the sun, so look out for windows that are constantly blacked out to cover that up. Cannabis farms in spare rooms will have the tell-tale sign of curtains that never open.

Heat Those lights also give off a lot of heat, so the old theory was that the house growing cannabis in the loft would be the one with no snow on the roof in winter. But nowadays growers use internal tents, that isolate a lot of the heat. This makes farms harder for police to spot using their infra-red cameras.

Ventilation Growers need to ventilate the plants with large extractor fans, which generally emit a low hum. If every morning, at exactly the same time, it sounds as if someone next door is starting up their hovercraft, then it's probably a cannabis farm warming up for the day.

Security Growers live in a paranoid world, always wondering when their door is going to get kicked in – not only by the police but by "enforcers", violent criminals who make their living by stealing cannabis crops. For that reason many of them adopt Fort Knox-like security. Portcullises on the doors, bars on the windows and even CCTV cameras are not uncommon.

Activity Not all farms are inhabited by the grower so watch out for signs that there is no one actually living there: unkempt front gardens, or if your neighbour never leaves out any bin bags on collection day.

Good neighbourliness If the grower is in residence then it can go the opposite way. Perhaps the most surprising tell for having a grower next door might be their over-the-top neighbourliness as they overcompensate in their efforts not to annoy you or make you suspicious as to what they're up to. As one grower told me: "I'm the nicest, most law-abiding citizen on my street, because the last thing I ever want is to give someone a reason to want to call the police to complain about me."

But you may not be the only person trying to spot a cannabis farm on your street. The sinister side to these booming businesses is that they have become lucrative targets for harder and more violent criminals looking to rob them. These people are constantly on the look out for farms within our communities, which in turn exposes the rest of us to potential violence. What's the solution? The dealers and criminals I spoke with all said that legalisation would put them out of business.

Conor Woodman's film Exposure: Britain's Booming Cannabis Business is on ITV on 16 October at 11.05pm

• This article was amended on 17 October 2013. A sentence had been added to the writer's original copy, which has now been removed.