A landlady was “devastated” to discover an organised crime gang had turned her five-bedroom rental home in Watford into a cannabis factory.

The woman, who does not wish to be named, found the tenants through the Gumtree website who paid the £1,600 rent every month without fail.

But she was unaware that equipment and plants, as well as someone to manage the cultivation, had been brought into the property.

A total of 420 cannabis plants, in various stages of growth, were found in the premises with an estimated yield value of around £100,000.

The landlady believed she was being “pranked” when police told her there was a cannabis factory in her home.

She said: “My first reaction when I got to the house was ‘it stinks’. We had to repaint the whole house and change all the carpets and soft furnishings to get rid of the smell. The police took all the illegal stuff but we were then left with a load of wires and pots to dispose of. The place was a wreck.

“The whole experience was scary and stressful; it wasn’t just the damage to the house, it was having to go through all the legal stuff. When I first got the call all I could think was how do I justify this? Am I liable? Will I go to prison? You feel guilty even though you haven’t done anything wrong. It was such a huge relief when they said they knew I had nothing to do with it.

“But after that I had to live with the worry; I’ve met these people, they are criminals and they had my details, my address from the rental agreement, could they find me and ask for their rent back? Are they going to hurt me or my family? It was a lot to deal with and months of watching our backs, worrying for the children and being suspicious on daily basis about anybody.”

Due to intelligence, Hertfordshire Constabulary’s Operational Support Group officers were able to shut the production down.

Three rooms and the loft at the house had been converted so the cannabis could be produced and the electricity meter had been “dangerously bypassed to power production”.

A Vietnamese national was subsequently arrested but treated as a victim of people trafficking by officers and placed into care due to his age.

The original renters were discovered to be Chinese nationals using fraudulent British passports as ID and fake copies of bank statements and pay slips.

They were never traced.

Sergeant Dave Perkins, from Hertfordshire Constabulary’s Operational Support Group, said: “Working alongside our partners, we are committed to making Hertfordshire a hostile place for organised crime groups to operate.

“However, we also need the public to assist us in our fight by reporting any suspicious activity and looking out for the tell-tale signs that a cannabis factory is operating in your property or neighbourhood.”

How to spot a cannabis factory:

• A strong and sickly sweet smell

• Lighting and ventilation equipment being taken into the house

• Windows always covered or blocked off

• People coming and going at all hours or neighbours you never see

• Strong and constant lighting at all hours

• High levels of condensation

• Constant buzz of ventilation equipment

• Lots of power cables around the property

If you suspect drug crime, contact police on the non-emergency number 101 or report information online at www.herts.police.uk/report.