Landlords should monitor the gardens of their rental homes after a court ruling allowed homeowners to sue their neighbours if Japanese Knotweed grows onto their land.

Neighbours Stephen Williams and Robin Waistell were each awarded £15,000 last year after knotweed spread from Network Rail land onto their gardens in Maesteg, Wales.

The court ruled that Japanese Knotweed is a ‘nuisance’ and ‘natural hazard’ that landowners must keep under control or pay the price.

Network Rail lawyers warned that victory for the neighbours could trigger an avalanche of similar damages claims.

Brought into Britain in the 19th Century as an ornamental plant, Japanese Knotweed now has a stranglehold on the country, and its devastating effects are so extreme that people can even be refused a mortgage.

Homeowners could face a fine or even a jail sentence if they remove it, but don't dispose of it properly, causing it to spread.

The government estimates the total annual cost of Japanese Knotweed to the British economy is £166 million in treatment and home devaluations.

It can grow through concrete and tarmac with roots going down as far as four metres.

It spreads at a rate of up to a metre a month and can cause structural damage to buildings and paths, cause walls to collapse, with roots that can crack or block underground drains and affect patios, driveways and paving.

Knotweed has a purple speckled stem, large lush-green shield-shaped leaves with a flat base that are arranged in a zigzag pattern along a hollow, bamboo-like stem and has distinctive white flowers in the summer.

Because it can spread very easily, proper treatment and disposal is vital.

Landlords are advised to carry out regular inspections of their rental homes to identify any potential issues. And if buying a property to rent out, they should factor in the cost of tackling the Japanese Knotweed problem, which can run to several thousands of pounds.

Landlords are also advised to hire a professional from either the Property Care Association or the Invasive Non-Native Specialists Association (INNSA) which both offer insurance-backed guarantees.

The issue of knotweed is so severe that the Home Office has reformed anti-social behaviour powers in a bid to tackle the issues.

Richard Truman, Head of Operations at Simple Landlords Insurance, added: “Inspecting your property is absolutely vital – and that has to mean going out into the garden, too. We know that a quarter of landlords haven’t inspected their properties in the last year. In that time, small issues can become big and potentially expensive problems – and that includes Japanese Knotweed.”