A major crackdown against suspected indoor cannabis farms and the criminal gangs who run them is under way.
Seventeen police forces across England and Wales are carrying out raids over the next two weeks on addresses where they suspect cannabis is being grown.
The gangs can make £30,000 in three months from a farm of just 200 plants and regard the ventures as relatively low risk but highly lucrative.
In January, the government decided to keep cannabis as a Class C drug.
But on Monday Home Office Minister Vernon Coaker said: "Those who use and sell cannabis will face tough penalties - up to 14 years for cultivation and dealing.
"We fully support this crackdown, which sends out a powerful message that growing and dealing in cannabis will not be tolerated."
Officers are searching a suspected cannabis farm at a house in Dagenham, while two other raids in east London found nothing.
Called to the property following reports of intruders trying to break in, Det Insp Neil Hutchison said there were about 100 plants.
The drug's classification had not affected officers' determination to tackle cannabis cultivation, he added.
And they were shutting about two farms every day in London alone.
The proceeds are used to invest in other crimes, Det Insp Hutchison said, and illegal immigrants are sometimes trafficked illegally to the UK in order to grow the cannabis.
Allan Gibson, of the Association of Chief Police Officers', said it was an "increasing problem which must be nipped in the bud".
He said: "Cannabis cultivation is seen by criminals as a low risk, high-profit industry, but this operation will send out a clear message that cannabis production is a serious offence and that offenders will be brought to justice."
The farms have started to appear in quiet residential streets, with figures showing that the amount of cannabis grown in the UK has risen from 10%, 10 years ago, to 60% now.
Huge electricity bills for halogen lighting
Gardening tools left outside
Windows covered all the time
In the UK, the type of drug which is mainly grown is known as skunk, a strong variant of the drug which is potentially harmful.
The gangs who run these farms often steal electricity using wiring set-ups which can carry a risk of causing fires.
Police want to raise awareness on the issue so that the public keep an eye out for the "skunk factories".
As well heavy usage of electricity to power the halogen lighting rigs used in cultivation, other signs of a possible factory are windows that are covered all the time, gardening equipment left outside or a pungent smell coming from the building.
Police are already using thermal imaging cameras to spot the factories, which can be up to 10 times hotter than a normal house because of the heat from the lights.