Bristol has maintained its status as England's primary Japanese knotweed hotspot, showing an infestation density over twice that of any other region. Analysis by Environet identified 1,324 incidences across the city, equating to 32.29 per square mile.
Merseyside followed with 13.45 incidences per square mile, while Greater London recorded 7.67. Greater Manchester and Lancashire completed the top five, with 7.49 and 7.00 incidences per square mile respectively.
The rankings are based on over 100,000 verified sightings from Environet’s Exposed: The Japanese Knotweed Heatmap. Former docklands and industrial areas are prominent in the rankings, which Environet attributes to the historical movement of contaminated soil.
Environet estimates that Japanese knotweed impacts 7% of UK homes, affecting more than 1.58 million properties. Research suggests an infestation typically reduces a property's value by approximately 5%, or £13,500. The invasive plant can also hinder property transactions, cause damage to buildings, and lead to legal disputes if it spreads across boundaries.