Environet UK has revealed the top Japanese knotweed hotspot in each region of Great Britain, using data mined from its online Japanese knotweed heat map.

Bolton in the North West is the area worst affected by the weed, with 652 infestations within a 4km radius.

The second most affected area is Bristol in the South West followed Capel Garmon in Conwy, North Wales. Clapham Common is the worst affected area in London.

Japanese Knotweed is described by the Environment Agency as “indisputably the UK’s most aggressive, destructive and invasive plant”, and it grows rampantly along railways, waterways, in parks and gardens and is notoriously difficult to treat without professional help.

Map your risk

Environet has analysed data from its online Japanese Knotweed Heatmap, launched earlier this year, which records Japanese knotweed sightings across the UK, to inform local homeowners and potential homebuyers of the local presence of the weed.

The top Japanese Knotweed infestation areas for each region are as follows:

North West: Bolton, Lancashire
South West: Bristol
Wales:Capel Garmon, Conwy
Yorks & Humber: Rotherham
East Midlands: Nottingham
London: Clapham Common
Scotland: Glasgow
West Midlands: Madeley, Shropshire
South East: Shanklin, Isle of Wight
East: Norwich
North East: Newcastle

Why it’s a problem

Japanese Knotweed can deter buyers, making a property difficult to sell and prevent a mortgage lender approving a loan, unless a treatment plan is in place with an insurance-backed guarantee. According to Environet UK, it can reduce a property’s value by around 10%.

Sellers are required by law to inform potential purchasers whether their home is, or has been, affected by Japanese knotweed, which can act as a deterrent even if the infestation has been treated.

Environet estimates that Japanese knotweed currently affects 4 to 5% of UK properties, wiping a total £20bn off house prices.

Nic Seal, founder of the business, said: “Japanese Knotweed has become a major problem across the UK, with areas of industrial heritage such as Bolton and North Wales particularly badly affected.

“Anyone thinking about buying a property in or around these hotspots would be wise to check the number of infestations in the proximity of their postcode and consider instructing a specialist to carry out a survey on the property to check for evidence of the plant.”

You can view known Japanese Knotweed infestations in your area or report a sighting using Environet’s heat map at https://environetuk.com/exposed-japanese-knotweed-heat-map-information.