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How do police find grow houses in the UK?

cannabis cultivation

Across the world, the past decade has seen the liberalisation of laws prohibiting the production, sale, and consumption of cannabis. However in the United Kingdom, cannabis remains a prohibited drug, with the exception of limited prescriptions for medical use. Growing cannabis in the UK can result in a substantial custodial prison sentence. Nonetheless, it is a budding industry (excuse the pun) and between 6000 and 7000 individuals convicted for commercial cultivation each year between 2009 to 2014. This article explores the law surrounding growing cannabis in the UK. We look at what criminal offence this falls under. We also explore how the police identify growing operations in the UK, and the sentence that you could face if you are convicted for growing cannabis.

Is cannabis a controlled drug in England and Wales?

Cannabis is a Class B controlled drug under Part II, Schedule 2 of the Misuse of Drugs Act 1971. Other legislation that addresses the prohibition of cannabis includes:

These laws make is unlawful to cultivate, possess, supply, produce, import or export cannabis without a Home Office licence.

Cannabis based products for medicinal use in humans are exempt from prohibition. These products are defined in Schedule 2 of the Misuse of Drugs Regulations. You need a licence in order to lawfully cultivate, possess, supply, produce, import or export medicinal cannabis products.

It is also possible to obtain a licence for the production of cannabis for hemp products such as hemp fibre or oil. These products must be classified as low tetrahydrocannabinol (THC) in order to be capable of receiving a licence. This is defined as THC content not exceeding 0.2%. CBD products are also controlled under the MDA 1971/2001, however they are not illegal.

What is the criminal offence for having a grow house?

If you are arrested for having a grow house, you will most likely be charged under either Section 6 of the Misuse of Drugs Act, which restricts the cultivation of cannabis, or Section 4, for production of a controlled substance. The interpretation section of the Act specifies that production includes cultivation of cannabis plants. The two offences carry the same maximum sentence.

However, the Proceeds of Crime Act 2002 applies to the production offence, which means that the court is allowed to make a confiscation order where the defendant is shown to have benefitted from their criminal conduct. Generally, smaller scale operations that are principally for personal use will be charged under cultivation, whereas larger scale commercial operations will be charged under production.

It is also an offence to allow premises to be used for the cultivation of cannabis where you are the owner, manager, or occupier.

How do police find grow operations?

Police use a variety of tactics to identify cannabis grow operations. Police may be notified where there is a very high utility usage – such as electricity and water, and check to see if there is illicit cultivation underway. This is because the lights, dehumidifiers, hydroponic systems and heaters used to grow cannabis use a significant amount of electricity.

Police may also use infrared to identify a warmer building, due to the lighting that is used to grow cannabis plants.

According to the National Police Chiefs Council (NPCC), many police operations to uncover cannabis factories are intelligence led. This means that they rely on tip-offs from members of the public or police informants. Police also use open source internet research, via their dedicated cybercrime teams to identify online activity linked with cannabis cultivation and sales.

Another way in which cannabis factories have been discovered is through fires breaking out at the properties. According to the NPCC, this is most likely due to cannabis producers bypassing the electricity and gas meters in order to obtain utilities without paying for them.

According to crime stoppers, known signs of a grow house include:

  • The smell of cannabis in the vicinity of the grow house
  • Frequent visitors throughout the day and night
  • Covered or blacked out windows
  • Chinks of bright light throughout the night
  • Birds gathering on the roof, particularly in cold weather
  • If it has snowed, the snow melts more quickly on this roof compared with surrounding buildings
  • High levels of condensation on windows
  • Noise from fans
  • Large volumes of rubbish, including garden compost
  • Signs that the electricity meter has been tampered with or new cabling has been put in, often connected to street lighting

Other giveaway signs of a grow house include excessive security on the building such as padlocks, grilles, CCTV cameras, portcullises, bars on the windows, and extra locks.

What is the sign of a grow house?

Grow houses can be located in a variety of buildings. Domestic dwellings are the most popular location, accounting for 9% of all commercial cannabis factories. Industrial commercial properties account for around 7% of all cannabis factories. Farm/agricultural locations also form a significant proportion of cannabis factories.

Grow houses have been linked with modern slavery, particularly of Vietnamese illegal immigrants, who are often under pressure to repay people smugglers upon their arrival in the UK. Through participating in growing operations, they are able to work illegally to repay their debt. However, working conditions are often very exploitative and there are links between cannabis factories and human trafficking.

What is the punishment for having a grow house?

Both the production and the cultivation of cannabis are either way offences, which means that depending on the seriousness of the offence it could be heard in the Magistrates’ Court, where the maximum custodial sentence is twelve months, or it could be sent to the Crown Court.

The maximum sentence that you could receive from the Crown Court is 14 years’ imprisonment. The normal sentence range varies from a discharge to a 10 year prison sentence.

When deciding the appropriate sentence, the court will look at the culpability (blameworthiness) of the offender, and the harm caused by the growing operation.


The court will be seeking to determine whether the offender played a leading role, significant role, or minor role in the grow operation. Was the offender directing or organising the operation? Did they have a substantial influence over others in the operation? Were they expecting to receive substantial financial gain? Were they using a legitimate business as a cover for their grow operation? These factors would all tend towards a leading role. A significant role might include a middle management function in the grow house, or pressurising others in the operation to perform their roles. Someone in a lesser role could be engaged by pressure, coercion or intimidation. For example, an illegal immigrant working in exploitative conditions would be likely to be considered to be performing a lesser role.


The assessment of harm will simply be concerned with the number of plants cultivated as part of the operation. A domestic operation is 9 plants or fewer. An operation producing more than 28 plants will be considered to be capable of producing significant quantities for commercial use.

Examples of possible sentences

The following examples give the sentence starting point in different scenarios. However, note that the starting point sentence will be adjusted on a case by case basis to take into account aggravating and mitigating circumstances.

  • A grow operation with 50 plants where the offender is in a leading role has a sentence starting point of 8 years
  • A grow operation of 15 plants where the offender is in a minor role would result in a sentence starting point of a high level community order
  • A grow operation of 2 plants would be considered to be for domestic use only. At worst, you could receive a one year custodial sentence. At best, you could receive a discharge or a fine.

The disparity in sentencing between the most serious and least serious cases of cannabis production/cultivation means that it is worthwhile having the best possible criminal defence solicitor represent you, even if you intend to plead guilty.

Where to get further information

Have you been arrested or charged with an offence linked to the production or cultivation of cannabis? If so, understand that if you are convicted of the commercial production of cannabis, you are probably facing jail time. Instructing a criminal defence solicitor in whom you trust could have a significant impact on reducing your sentence. At Stuart Miller Solicitors, if you decide to plead guilty, we will make sure that the court understands the nature of your extent and role in the cannabis cultivation, and whether it was for personal or commercial use. In doing so, we will help you obtain the fairest possible sentence. If you decide to plead not guilty, we will assist you in preparing your defence. Contact us for a no-obligation consultation today.


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