New figures have prompted calls for landlords to tighten checks on commercial tenants. They follow a sharp rise in cannabis farms operating from rented properties.

Some property owners have faced six-figure repair bills.

Zurich UK obtained data showing that fire service callouts to cannabis farms have more than tripled over the past decade.

There were 17 callouts in 2015. That increased by 218% to a record 54 in 2024.

Incidents remained close to that peak in 2025. Fire services recorded 50 attendances during the year.

Meanwhile, Zurich’s Claims Investigation Unit has investigated 17 cannabis farm-related claims since January 2022. Together, they were worth £9.4m.

The figures highlight a growing risk for landlords and managing agents. Organised criminal groups are targeting empty shops, offices and other commercial premises.

Cannabis farms leave extensive damage

Criminal groups can make extensive and dangerous alterations to properties used for cannabis cultivation.

They frequently tamper with electrical systems to meet the high energy demands of growing operations. Irrigation equipment can also cause serious water damage, damp and mould.

Unauthorised internal alterations and ventilation systems can cause further problems.

As a result, landlords can face months of reinstatement work. Tenants may not be able to occupy the property safely during this period.

Freedom of Information responses came from 21 fire and rescue services. They show incidents increased by 59% between 2019 and the 2024 peak.

South Wales Fire and Rescue Service recorded the highest number. It attended 90 suspected or identified cannabis farms over seven years.

Essex County Fire and Rescue Service attended 56 over the past decade. Hereford and Worcester Fire and Rescue Service recorded 55.

Separate Home Office analysis identified 640 cannabis farm fires across the UK between 2019 and 2024.

Scott Clayton, head of claims fraud at Zurich UK, said: “Many landlords still picture cannabis farms operating in remote industrial estates or hidden warehouses.

“What we’re increasingly seeing is organised criminal groups targeting empty shops, offices and retail premises, often hiding in plain sight on high streets across the UK.

“These operations can involve sophisticated attempts to present a legitimate business front, making it difficult for landlords to spot the warning signs until significant damage has already been done.

“Our specialist Claims Investigation Unit has dealt with cannabis farm claims worth £9.4 million since 2022 alone, highlighting the scale of the problem.

“Robust due diligence, regular inspections and a willingness to question unusual behaviour remain some of the most effective ways landlords can protect themselves from a growing and costly threat.”

Stewart Powell, regional major loss lead at Zurich UK, added: “For many landlords the full impact only becomes apparent once a cannabis farm has been uncovered and the extent of the damage becomes clear.

“While the fire risk associated with these operations is well known, fire is often only one part of a much larger problem.

“We’ve seen claims involving dangerous electrical alterations, extensive water damage from irrigation systems, widespread damp and mould, and significant structural changes made to conceal growing operations.

“By the time a property is recovered, landlords can be left facing months of disruption, substantial reinstatement work and repair bills running into hundreds of thousands of pounds before a building can be safely occupied again.”

Warning signs for landlords and agents

Zurich said potential warning signs can emerge before a commercial tenancy begins.

Prospective tenants may offer to pay the asking rent without negotiation. Some may also seek high-value, long-term leases without using solicitors.

Requests to pay deposits or rent in cash can be another warning sign.

Landlords should also scrutinise identification that is difficult to verify. Newly incorporated companies with little financial history may warrant additional checks.

Agents should be cautious if prospective tenants try to remove inspection clauses.

Proposed business activities that appear commercially unrealistic can also raise concerns. Applicants with little evidence of previously operating commercial premises may also warrant closer scrutiny.

Once a tenancy starts, landlords and agents should continue monitoring the property.

Warning signs include premises that never appear to trade and tenants who repeatedly avoid inspections.

Blackout windows, excessive condensation and unusual odours can also indicate problems.

Landlords should also look for unexplained alterations to electrical systems, internal partitions or external ventilation.

Unusually high humidity can be another indicator. Approaches from councils or utility companies about unpaid bills may also warrant further investigation.