A Japanese knotweed infestation caused homeowner Charron Ishmael to take her neighbour, retired NHS consultant Dr Sheila Clark, to court over a dispute about the plant.

Charron Ishmael was selling her property but because of the presence of the invasive plant in her neighbour's garden, she had to knock �150,000 off the asking price of her �1.1m home, and the court dispute cost her �100,000 in legal fees.

Ms Ishmael, 50, claimed that her neighbour Dr Sheila Clark, 72, was aware that for years she had the invasive plant in her garden in Islington, north London, but took no action to have the plant dealt with. Japanses Knotweed has roots that spread out over a considerable distance at an alarming rate and in doing so can invade neighbouring properties.

As reported by The Mail Online, Ms Ishmael said the plant had forced her to reduce the asking price on her house, which had otherwise been valued at �1.1million. The house was finally sold for �950,000.

Where did Japanese Knotweed come from?

The plant was introduced to Britain in the Victorian era as an ornamental garden plant and it was used by the railway companies at the time to stabilise embankment soils.

What was found however was that the plant, when allowed to get out of control, has the power to undermine buildings. Its banboo-like roots or stems known as rhizomes can in theory undermine walls, fences and buildings. Bamboo plants can be equally if not more dangerous

Native to Japan, knotweed is considered an invasive species in the UK because, whereas in Asia these plants are controlled naturally by fungus and insects; they have no such natural enemies in the UK.

Like bamboo, knotweed is incredibly durable and fast growing. An infestation is incredibly difficult and expensive to eradicate. But if left to grow out of control it can invade all adjacent gardens and houses.

The plant's roots spread at an alarming rate (up to 12 inches per day) in search of water and nutrients and will grow even faster when there's lots of water present.

Charron Ishmael claimed at the Central London County Court that Dr Clark knew about plant but allowed it grow out of control. She has said that she had no other option but to take her neighbour to court because her neighbour would not control the knotweed and the local council refused to do anything about it.

The result has meant losing money on her house sale as well as a ruinous legal bill and her health has suffered having been signed off sick from work when the County Court case went against her, she claims.

Ms Ishmael told MailOnline:

'It's terrible. I don't know how I am going to pay the legal fees. I haven't lied. I haven't done anything wrong. All I've done is to try to protect my house. 'It's been one thing after another. I'm off work with the stress of it all. I've had sleepless nights. To be honest I don't think the judge listened to what I had to say. I feel that my reputation has been tarnished.'�

Ms Ismael whose family had purchased the property in a quiet street in Islington, north London for around �250,000 in 2000, said her family had enjoyed many happy years living in the four-bedroom house.

The estate agent claimed the house was worth �1.1 million, but the buyers reduced their offer after seeing their survey report. The new owner has said that Ms Ishmael had made sure the plant had been eradicated before the sale completed.

What RICS says about knotweed:

'Substantial structures on sound foundations are unlikely to suffer structural damage due to Japanese Knotweed.'�

It has been estimated that knotweed, a plant that is difficult to kill and irradiate, grows up to 10ft, and has been costing the UK economy millions a year in treatment and in home devaluations.

The plant tends to lie dormant in winter months before resuming its rapid growth in the summer, while there is a danger of it reaching buildings and crossing neighbour boundaries, sometimes resulting in litigation between property owners.

Government report on knotweed

A UK government report published last year gave credence to the view that Japanese Knotweed may not be as big a threat to buildings as previously thought. These were the conclusions reached in the government's report and pointed to what the future might hold for Japanese Knotweed and those affected by it.

Previous to that, in May 2019 the House of Commons Science and Technology Committee published a report 'Japanese Knotweed and the built environment'�. This followed a detailed inquiry prompted by the publication of new research by Dr Mark Fennell, Professor Max Wade and Dr Bacon in July 2018 (Fennell et al) which suggested that Japanese Knotweed may pose no greater threat to property than that of other plants.

What exactly is Japanese Knotweed?

It is a large, highly aggressive and invasive weed, sometimes referred to as 'elephant ears, 'donkey rhubarb'� or 'monkey weed'�. It grows in a variety of conditions and can commonly be seen alongside train tracks, on river banks and on waste ground.

The plant has large hollow stems similar to bamboo and large, green, heart shaped leaves. Its roots (rhizomes) have been thought to grow as far as seven metres horizontally and two metres deep underground '� it is this extensive root spread that makes the plant so difficult to remove once established.

The only means of destroying Japanese Knotweed is to kill the roots. This can only be achieved by either multiple applications of herbicide or full excavation. If even a few centimetres of root are left in the ground, the plant can regrow.

Japanese Knotweed is classed as a controlled plant under the Wildlife and Countryside Act 1981.

Whilst it is not illegal to have the plant on your own property, it is illegal to allow it to spread on to adjoining property, including allowing the roots to spread underground. Under the Environmental Protection Act 1990 the plant is classed as 'controlled waste'�, meaning that it is illegal to dig it up and remove it from your property unless it is disposed of at a licensed landfill site.

A landmark legal case

In a 2018 legal case, Network Rail Infrastructure Ltd v Williams and another involved Japanese Knotweed growing on a railway embankment owned by Network Rail, and the claimants owned affected bungalows.

The Court of Appeal made it clear that the presence of knotweed will not, in itself, provide grounds for a diminution of value claim, but encroachment of the plant onto neighbouring land will probably entitle the neighbour to damages. This is not because of any reduction in value, but because it interferes with the ability to fully use and enjoy the land. It has yet to be seen how courts would approach the quantification of such loss, but the above case may or may not be a good example.

Mortgage lenders have some concern about knotweed and its impact on the built environment. But stories about knotweed have become a popular media favourite, often exaggerated. It can undoubtedly damage the built environment, but usually in buildings by exacerbating an existing weakness such as cracks, crumbling mortar, decaying tarmac etc. It can lift paving slabs, block paving, etc, but damage to building structures is rare.