A national police crackdown on illegal cannabis factories was launched today.
The operation involves close to 20 police forces in England and Wales and is expected to last for two weeks.
Cannabis factories will be closed down by police and the criminal networks who run them disrupted and dismantled.
The Association of Chief Police Officers (Acpo) is expected to announce further details of the crackdown later this morning.
Alan Gibson, Acpo's lead on cannabis cultivation, said: "Cannabis cultivation is an increasing problem which must be nipped in the bud.
"This operation will see police closing cannabis factories across the country, arresting those concerned and using the Proceeds of Crime Act to attack the criminal profits being made.
"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.
"Not only is the money from cannabis cultivation ploughed back into serious crime, but the bypassing of the electricity needed to run the factories causes risk of fire and electrocution and they have already caused several devastating fires."
As part of the operation, police are expected to ask the public to look out for telltale signs of cannabis factories being run from properties in their neighbourhood.
These include the windows of a property being permanently covered, gardening equipment left outside or a pungent smell emanating from inside.
Earlier this year, police in London began using thermal imaging cameras to reveal the locations of secret cannabis factories.
The hand-held devices detect the extreme heat caused by the lighting systems used in the intensive rearing of marijuana plants.
Properties where cannabis is being grown will release ten times the amount of heat of an ordinary family home.
Each is capable of producing hundreds of thousands of pounds worth of cannabis a year.
A total of 19 police forces are taking part in the crackdown including Cambridgeshire, Essex, Greater Manchester, Hampshire, Hertfordshire, Kent, Merseyside, Norfolk, Northumbria, North Yorkshire, Nottinghamshire, South Wales, South Yorkshire, Surrey, Sussex, West Yorkshire, Wiltshire and the Metropolitan Police.
The operation, code name Keymer, runs until October 5.
The crackdown is targeting the most potent and potentially form of cannabis, known as "skunk".
Skunk contains far higher quantities of the chemical THC than herbal or resin-based cannabis.
In the mid-1990s only around 10% of cannabis in the UK was skunk but in the last 10 years that figure has risen to around 60%.
Each cannabis plant is capable of producing an ounce and a half of skunk- grade cannabis and a typical cannabis factory houses between 200 and 800 plants and sometimes as many as 1,000.
A crop of 200 plants could produce as much as £30,000 of skunk every three months, meaning the larger factories are capable of producing nearly £500,000 of the drug every year.
Last year, police identified more than 700 cannabis factories in London alone.
Criminal gangs are attracted to cannabis production because it is seen as low risk compared with the Class A drug trade.
However, the next two weeks will see police across the country stepping up raids on suspected cannabis factories and action to dismantle the networks behind them. Many cannabis factories are run by Vietnamese gangs, but there are other nationalities involved.
The equipment needed can be purchased legitimately as it is used in other types of cultivation and a factory can cost as little as £20,000 to set up.
As part of the crackdown, police are asking residents to look out for tell-tale signs of a factory in their area and to contact them.
Home Office Minister Vernon Coaker said: "We fully support this crackdown which sends out a powerful message that growing and dealing in cannabis will not be tolerated.
"Those who use and sell cannabis will face tough penalties: up to 14 years for cultivation and dealing."
Police were searching a suspected cannabis factory at a house in Dagenham, east London, this morning.
Officers were called to the property last night after reports of people trying to break in. When they entered they found several rooms full of cannabis plants.
Detective Inspector Neil Hutchison said he suspected the intruders may have been trying to steal the plants. He estimated there were around 100 inside, which would have been capable of producing around £15,000 of cannabis every three months.
Mr Hutchison said cannabis production was "a serious crime" and the reduction in classification of the drug had not affected the determination of police to tackle the trade.
He estimated that police were closing around two factories in London every day.
Asked why cracking down on cannabis production was a priority for police, he said: "Firstly, skunk is very strong. There is medical evidence to suggest that it can be damaging to mental health.
"Secondly, it is linked to organised criminality and if organised criminals are making large amounts of money that is bad for everybody, not least because they often invest it in other forms of criminality i.e. Class A drugs.
"Thirdly, it is linked to people trafficking, because a lot of people who grow the cannabis are illegal immigrants who are brought into this country to do that.
"Fourthly, it is a public safety hazard. They tap into the electricity cable prior to it getting to the meter. The properties are festooned with wires and electrical boxes. They are a hazard, they cause fires.
"Cannabis production is a serious crime. The reduction of the classification of possession does not in any way affect how seriously we take the cultivation of the drug."
Skunk cannabis is four to seven times stronger than normal cannabis and is linked to psychosis, depression and anxiety.
The masterminds behind the factories are "organised gangs with knowledge, finance and equipment" who are prepared to use violence to protect their money-spinning trade, according to Metropolitan Police Commander Allan Gibson, The Association of Chief Police Officers' (Acpo) lead on cannabis cultivation.
At least three murders have been linked to the trade.
Mr Gibson said: "Skunk tends to be home-grown and is about 60% of the cannabis available.
"A typical domestic factory will cost about £20,000 to set up and then can generate about £100,000 to £150,000.
"A very large factory in an industrial or agricultural unit can generate millions in a year.
"The largest we broke up was generating £8 million a year."
A small factory could have about 200 plants with about 1,000 plants being grown in a large factory.
Last year, London Fire Brigade reported about 50 house blazes linked to dangerous makeshift connections to help run skunk factories, Mr Gibson said.
"I don't know about the (fire hazard) figure nationally but you could probably double it," he added.