Do YOU live in a Japanese knotweed hotspot? Interactive map reveals locations in England suffering with the worst infestations of invasive plant

It is the bogeyman of the plant world and the bane of homesellers, an invasive species that destroys all vegetation in its path, can grow beyond the height of a double-decker bus, and snakes through the gaps in concrete and brickwork with insidious ease.

And the bad news is that Japanese knotweed is not just coming to a neighbourhood near you – it's probably already there, or at least nearby.

For the past six years, the prevalence of the ruinous plant has been monitored by Environet, a British company that specialises in the removal of invasive plants from residential and commercial properties.

Using an interactive online tracking tool, the firm has created a heatmap of verified sightings of the perennial that allows homeowners and homebuyers alike to keep abreast of the threat.

The map allows members of the public to report Japanese knotweed sightings by uploading a photo for verification by experts.

The picture that emerges is a sobering one, with at least one occurrence every three square kilometres in England and Wales.

Bristol and Merseyside lead the way, with 5.18 and 2.49 incidences per square kilometre, followed by Greater London on 2.29. Other hotspots include Greater Manchester, Lancashire and the Channel Islands.

'With over 60,000 known infestations of Japanese knotweed on our heatmap, we have a clear picture of its prevalence across the UK,' said Emily Grant, Environet's director.

'Knotweed is easily identifiable during summer, but it's a perennial plant, so as we head through the autumn and into winter, the above-ground growth dies back and it becomes much harder to spot.'

Now is the time to act, however, while cooling temperatures and fading light cause leaves to drop and brittle stems to snap, forcing the plant into retreat. Come spring, the plant will burst back into life.

It is estimated that approximately 5% of British homes are affected by Japanese knotweed, whether directly or by a neighbouring property.

One belongs to Edith James, 84, who recently entered a care home, leaving behind a three-bedroom semi-detached house in north Yorkshire that is infested with knotweed.

At a moment of emotional upheaval for the family, Edith's daughter, Christine, faces the unenviable task of explaining why they must now foot a £10,000 bill to deal with the problem or be left with a property worth 'next to nothing'.

'It's just a huge headache,' said Christine. 'You cannot sell a house without saying that you have knotweed. It will need a full refurbishment, and I'm very aware that you can't even get a mortgage on a property that's affected by it.

'It's in a good area, and when the house is done up it'll be a lovely family home, in a good part of Yorkshire, in a quiet location.'

Although Edith has owned the house since the early 70s, the family had no inkling of the problems that lay ahead until shoots began to appear in the garden.

Fearing the worst, Christine submitted a photo to Environet, who confirmed her worst fears. Nonetheless, her prompt action is expected to keep the plant at bay for at least a decade, affording any future buyer reassurance and ensuring the house will not need to be sold off at auction at a fraction of its true value.

'If you do have knotweed on your property, it's wise to act immediately to treat or remove it before it has the chance to spread further,' said Grant, who believes all buyers and sellers should consider a Japanese knotweed survey.

'With professional assistance, knotweed can be dealt with and the value of a property largely restored.'

The presence of knotweed near ports such as Bristol and Liverpool is believed to result from historical shipping and trading practices.

In the 19th and 20th centuries, ships returning to the UK often carried ballast, including foreign soil containing plant material.

The soil was typically discarded to make room for the next cargo, and was spread further in industrial areas such as Greater Manchester as a result of mining and other activities.

Knotweed first arrived in Britain during the Victorian era, when it was used as an ornamental garden plant and to stabilise the soil around railway tracks.

Now that mistake is coming home to roost.