Work started this week on a site for a housing development in Chalfont St Giles previously infested with “pernicious” Japanese knotweed.

Whether the weed is as pernicious as previously thought is now being questioned.

The developer, who doesn’t want to be named, bought the land in a probate sale in November last year. 

He plans to build three detached houses to replace the existing house which had been empty for several years.

Before the sale went through, fallopian japonica, to give it its Latin name, was discovered covering an area of 431 sq ft (40 square metres) on the 12,917 sq ft (1,200 sq m) site. 

The Environment Agency describes the horticultural invader as “indisputably the UK’s most aggressive, destructive and invasive plant.” 

Experts say it can grow in height at a rate of ten centimetres a day in summer.

Last week the Court of Appeal unanimously dismissed an appeal by Network Rail in favour of two homeowners who claimed the presence of the weed on the land adjoining their properties constitutes an actionable nuisance if it threatens to cross the boundary, even if it hasn’t yet. 

Just the fact the knotweed rhizomes are present constitutes an interference, said the judges.

Nic Seal, founder and MD of Environet, the UK’s leading specialist in the removal of the thug and the company commissioned by the developer to get rid of the knotweed in the Chalfont St Giles garden – said Network Rail had fought the original case thinking they could win and stem the tide of claims against them. 

“They’ve now scored two spectacular own goals and unwittingly opened the flood-gates for thousands of new claims,” he said.

“This judgment should put all owners of land infected with knotweed on notice to take proper action to ensure their knotweed does not encroach onto or threaten other property.”

The weed at the Chalfont St Giles property was well established due to the house being unoccupied for a lengthy period but as infestations go, it was relatively small. 

Building contractors were already on site with excavators to do the ground works for the three houses.

A spokesman for Environet told the Bucks Free Press: “The fastest and most efficient way to tackle the problem was for us to work in partnership with the house builder to supervise and guarantee the removal of the weed.”

The site was cleared of the plant in two and a half days. A ten year insurance-backed guarantee was issued to the developer, covering the cost of further treatment “in the very unlikely case that the knotweed returns.”

Work on site resumed this week. The builder said: “Japanese knotweed is a pain but I was pleased to learn that treatment methods have moved on considerably in recent years. 

“We didn’t waste any time in tackling the issue by having the knotweed physically removed from the site. 

“It took just two and a half days. Although the weed will be declared in the legal pack for buyers, as we have a ten year guarantee for the treatment work, I don’t anticipate it affecting our ability to sell the homes.”

The guarantee will be passed on to the buyers.

Up until now, the stigma attached to knotweed has affected property values. 

If the alien intruder is identified in the homebuyers survey, mortgage lenders want evidence that a treatment programme is in place to root it out. 

However, the strength of the case against the weed was questioned this week with the publication of a study by ecologists from global infrastructure services firm AECOM and the University of Leeds. 

Following the “most extensive research to date to assess the potential to cause structural damage compared with other plants,” AECOM’s chief ecologist Dr Mark Fennell stated: “We found nothing to suggest it causes significant damage to buildings even when it is growing in close proximity and certainly no more damage than other species that are not subject to such strict lending policies.”