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Japanese knotweed: what estate agents need to know

When it comes to property, ‘Japanese knotweed’ are the two words most homeowners and prospective buyers do not want to hear. 

With a knotweed infestation estimated in every 10km2 of the UK, this non-native plant is able to push through cracks in concrete and tarmac, and undermine building structure. If left untreated for a prolonged period of time, Japanese knotweed can pose a threat to property valuations.

The knotweed problem, however, is not confined to just the buyer and the seller in a property transaction. In fact, there are 10 stakeholders involved, each with varying levels of responsibility and liability. 


With the estate agent at the heart of the transaction, and expected to offer advice, they need to understand each stakeholder’s responsibilities at every stage. Not only with this help the sale go through smoothly, it will also ensure their reputation is kept intact.  

1) The estate agent 

The priority for estate agents should be ensuring that Japanese knotweed does not threaten the sale. First, and most importantly, estate agents are legally required to inform a prospective buyer if knotweed is present on the property, as this may affect their decision to buy. 

If knotweed is present, agents should advise the client making the sale to quickly implement a treatment strategy with a reputable remediation firm, so that buyers are reassured that the issue is under control.  

Before informing a prospective buyer of the presence of knotweed, however, estate agents should always refer to an expert for confirmation. 

Even identifying knotweed can pose problems, due to its similarity in appearance to other plants. In the worst cases, misidentification can lead to the devaluation of properties.   

2) The seller 

The seller is legally obligated to declare if knotweed is present on the land. Introduced in 2013, the Law Society’s TA6 property information form now specifically asks “is the property affected by Japanese knotweed?”. 

Estate agents should make sure the seller is aware of the implications of non-disclosure, which could result in them being sued.

If knotweed is present, estate agents should advise the seller to look for a remediation firm that offers a warranty for completed work which is protected by an independent insurer. This will provide the seller (and the buyer) with peace of mind that the property is protected if knotweed regrows after treatment, and will also prove to the conveyancer that the knotweed issue is under control. 

3) The buyer 

If the buyer has done their due diligence, they will be vigilant against knotweed and will not want to purchase a property with an infestation. Estate agents need to be armed with the facts on what remediation strategy is in place, so the buyer is not deterred.  

4) The builder 

Unlike existing properties, the TA6 form does not apply to new build houses. This means that housebuilders are under no legal obligation to actively declare if the site has any historical knotweed issues, which could result in disgruntled new homeowners if any problems do arise. 

Estate agents should be aware of this, and advise the buyer to directly pose the question to the builder. 

5) Neighbours: both commercial and residential

Japanese knotweed can be a source of neighbourly disputes, and property owners who fail to control knotweed can be issued with an anti-social behaviour order. Often the dispute arises over who should pay for treatment if knotweed has spread from one property to another. 

Estate agents should advise the seller to come to an agreement with neighbours regarding the allocation of costs for remediation. 

Agents need to be aware of commercial neighbours as well as residential. Last year, Network Rail lost a court battle against a resident after knotweed infested his land from a nearby railway embankment. Legal disputes can be very messy for house sales, and again, can deter a prospective buyer.

6) The conveyancer or solicitor  

If a property does have knotweed, the conveyancer or solicitor will require proof from the seller that it is under control. If they are dealing with a builder, they need to ask whether there are historical knotweed issues on site if requested to do so by the buyer. 

A failure to do so could result in the solicitor being sued for professional negligence if knotweed is present. If they are a partner solicitor of the estate agents, this could reflect badly on the agent and damage their reputation. 

7) The surveyor 

The buyer will expect the surveyor to identify Japanese knotweed if it is present. If the plant is flagged up, it could have implications for the mortgage valuation. Often, the buyer’s survey is conducted towards the end of the transaction process. The discovery of knotweed at this point can cause considerable delays, and estate agents should be prepared for this possibility. 

Moreover, if the surveyor is the estate agent’s recommended partner and they fail to notice knotweed, this could discredit both parties.  

8) The insurer 

Specialist insurance should be in place for treatment work conducted by the remediation firm. This will reassure all parties that the property is protected in the long term if knotweed regrows.   

9) The mortgage lender 

Lenders may be cautious about lending against a property that has knotweed, due to possible reductions in property value. Many lenders will require a knotweed management plan to be in place so the value of the house will not be affected. This is why it is important for the estate agent to be advising the seller on a plan of action as soon as possible. 

10) The remediation firm 

The remediation firm needs to treat the plant effectively in the first instance, and should hold the insurance backed warranty to protect the customer in the long term. 

In a market plagued by cowboy remediation companies, estate agents should be able to offer advice on which firms are reputable. 

At every stage, estate agents can play a role to ensure that each stakeholder is satisfied that knotweed does not have to impinge upon the transaction as much as initially thought. 

In understanding the full process and responsibilities of all parties, agents can progress proceedings more quickly and make sure the sale goes through smoothly. 

For more information about Japanese knotweed, visit: https://www.japaneseknotweedcontrol.com

*David Layland is the joint Managing Director of Japanese Knotweed Control Ltd., and is a founding member of the Invasive Non-Native Specialists Association


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