The invasive plant specialist said the problem could further exacerbate conveyancing bottle necks and long delays already being experienced by buyers and sellers rushing to meet the stamp duty holiday deadline.

It said a total of 474,849 sales were agreed during Q3 2020 – 53% more than over the same period in 2019, prompting groups such as the Conveyancing Association to issue warnings of delays in the conveyancing process.

But with Japanese knotweed thought to affect around 5% of UK properties, either directly or indirectly, nearly 24,000 deals already agreed could face further complications and delays, Environet warned.

It said buyers were particularly vulnerable at this time of year as the plant’s above-ground growth died back, making it more difficult for a surveyor to identify and much easier for sellers to conceal.

Detection dogs

The only way to know with a high level of certainty whether a property was affected by knotweed, Environet explained, was to commission a dog detection survey which can be carried out during winter, since the dogs are trained to detect the unique scent of knotweed rhizome, even when hidden beneath the ground.

Environet’s detection dogs can cover a garden in a matter of minutes and will indicate by freezing if knotweed is detected.

Dog detection surveys are useful to sellers of homes that have been affected by knotweed in the past, or which are located in a high-risk area, who wish to reassure buyers that the property is free of the invasive plant.

They’re also useful to buyers who have concerns that a property they wish to buy might be affected, especially if the seller has answered “not known” in response to the Japanese knotweed question on the TA6 conveyancing form, completed as part of the property sale process.

Nic Seal, founder and MD of Environet, said, “As we head into the winter months with the property market far busier than usual, there are thousands of deals already agreed which could be delayed further by Japanese knotweed, risking the possibility of missing out on stamp duty savings.

“Japanese knotweed is dying back at this time of year and before long all that will remain is some dead-looking canes which are easily removed and concealed, making it harder for buyers and their surveyors to identify the plant.

“The best way to prevent knotweed delaying a sale is to be up front about it from the beginning and ensure there’s a professional plan in place to satisfy a buyer’s mortgage lender. And if you’re unsure if a property you’re buying or selling is affected, call in the detection dogs to find out either way with a high level of certainty.”