While some cannabis grows will be for personal use, many are part of a network of farms, masterminded by criminal gangs.
Police say that criminal gangs are increasingly renting out suburban homes to convert into cannabis factories.
And they are urging people to be wise to any suspicious goings-on in their neighbourhoods.
Luckily, there are plenty of tell-tale signs which can alert people to a hidden cannabis farm on their street.
Here's a list of some of the most obvious signs that a neighbour might be growing cannabis:
1. There's a strong, sickly smell.
It might sound obvious, but most cannabis grows are discovered by passers-by or keen-nosed residents catching a whiff of the drug's familiar smell. Police have even handed out scratch-and-sniff cards to help people recognise the scent.
2. High levels of condensation
Landlords might notice damp on the walls or peeling wallpaper, while from the outside a neighbour might spot condensation on the windows, even when it's not the depths of winter. The condensation may well be due to inside having been turned into a makeshift greenhouse.
3. Constantly covered or blacked-out windows
Do they have the curtains drawn all day long? Or have they put black-outs over all the windows? It might make it look like the house is unoccupied, but blacked out windows could well mean inside is really, really bright with all those strong lights.
4. Cannabis growing equipment transported to and from the house
Thousands of pounds worth of equipment is often needed for large-scale grows - have you seen lots of things being delivered to the house, or large items being taken in or out?
5. Constant buzz of ventilation
If you can hear the constant noise of a fan, at all times of the day or night, chances are it could be acting as ventilation for the cannabis grow.
6. Strong, constant lighting day and night
Cannabis needs light to grow, so watch out for homes with bright lighting at all times of the day and night. Lights will often be on a timer switch, coming on in the middle of the night.
7. Lots of power cables and rocketing electricity bills
The lights, dehumidifiers and heaters take a lot of electricity. Growers will often hack into the electricity wires before the meter to that individual house, and so bypass having to pay for the electricity.
If you are a landlord who gets a copy of the bill, has it dropped suddenly, or gone up suddenly? If you are a neighbour and your bill has rocketed – maybe your next door neighbour has hacked into your mains and you're paying to grow their drugs?
8. Heat, birds on the roof, or a lack of snow
Cannabis factories produce a lot of heat, which can cause tell-tales signs, especially in winter. When it snows, the roofs of cannabis farms can be obvious as the snow melts, meaning it is probably the only house on the street without a snow-covered roof. Birds also like roosting on a nice warm roof...
9. Unsociable comings and goings
Are there lots of unfamiliar faces turning up at the house at any time of the day and night? It could just be a popular family, but maybe it's something more sinister.
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