Incidents have been marked on a heatmap created by Environet, a company that specialises in the removal of the destructive and invasive plant.
The worst affected areas are Bristol, Bolton, London and South Wales, according to the map.
Anyone can report a sighting of the plant on the map, which is then verified by Environet.
Property professionals, including mortgage brokers, developers, surveyors, conveyancing solicitors and estate agents have been encouraged to use the map to help assess the level of risk posed to a property or site.
Japanese knotweed is notoriously difficult to treat and can impact a property’s value.
Users enter a postcode into the ‘Exposed’ tool to find out the number of reported knotweed sightings nearby.
Nic Seal, founder and managing director of Environet, said: “We’ve had an incredible response to the launch of Exposed, with over 100,000 visits during the first year and 93,000 postcode searches.
“This just goes to show the thirst for information about Japanese knotweed and the need for credible resources to help property professionals and their clients assess risk during the buying and selling process.
“High risk results should always prompt further investigation with an on-site Japanese knotweed survey, in order to give the buyer as much certainty as possible.”