Patent destroying disclosure – a concerning lesson from the case of Claydon YIELD-O-METER Limited v Mzuri Limited et al [2021] EWHC 1007 (IPEC). In this case the inventor’s outdoor use of agricultural equipment, despite being on a private secluded field was a prior public disclosure, and so the invention was not novel. The case highlights the importance of avoiding prior public disclosure, but raises the practical question of how can you ever confidentially test and develop large machinery?


The case concerned two of Claydon’s patents relating to agricultural machinery known as ‘seed drills,’ which are attached to tractors to sow seeds with precision. Mr. Claydon, the inventor, was also a party to these proceedings. Before filing the patents, Claydon had tested the invention on his own private fields with the help of his brother. The focus of the case for our consideration was whether those tests in those fields, could have enabled someone to see the invention before it was patented. The case was brought by Claydon who claimed that Mzuri’s seed drills infringed both its UK and European patents, who in defence attacked the validity based on prior use disclosure. Hacon HHJ held that whilst Mzuri’s seed drills would have infringed Claydon’s patents if they had been valid, the patents were invalid in light of the public disclosure by Claydon before the patents’ priority dates.

The law on prior use

An invention is novel if it does not form part of the state of the art. Section 2(2) of the Patents Act 1977 states that:

The state of the art in the case of an invention shall be taken to comprise all matter (whether a product, a process, information about either, or anything else) which has at any time before the priority date of that invention been made available to the public (whether in the United Kingdom or elsewhere) by written or oral description, by use or in any other way.

It is settled law that there is no requirement for anyone to have actually seen the prior disclosure for it to be considered part of the state of the prior art. For example, it is sometimes argued that the book on the library shelf may be considered a prior disclosure if no one has actually ever read it.

The decision

In finding Claydon’s patents to be invalid, Hacon HHJ referred to the recent judgment in E. Mishan & Sons Inc. v Hozelock [2019 EWHC 991 (Pat), (the ‘Hozelock’ case), and the tests set out in that case.

In Hozelock, Mr. Justice Nugee had to decide if the use of a prototype hosepipe in the inventor’s private garden amounted to prior public disclosure, given that the garden was visible to the public.  On the facts in Hozelock, it was held that as the inventor was aware of the danger, he would have taken the hosepipe inside as soon as he became aware of anyone trying to watch him in his garden. On that basis, Mr. Justice Nugee held that there was no potential for a public disclosure, as the inventors did not intend to ever disclose the hosepipe.

In contrast, in the present case Hacon HHJ found that even if the inventor had been aware of the possibility of a passer-by, the inventor would not have been able to move the equipment indoors, or to have taken sufficient action to conceal the claimed features of the seed drill, given its considerable size.

In his judgment, applying the principles set out in Hozelock, Hacon HHJ pays careful consideration to the specific surroundings. For example, how high was the hedge? How had the view of the field changed? Would a passer-by from the path have been able to view properly the tractor given the angle? And so on.

In particular, Hacon HHJ stated that “If Mr. Claydon or his brother had noticed such a person [on the path], I do not believe that Mr. Claydon could have taken action that would have prevented the skilled person from seeing or inferring each of those features, including the alignment of the tinesMr. Claydon had to test his prototype, nobody saw any of the testing and I entirely understand why he believed that his invention was not publicly disclosed. Unfortunately for him, in law the prototype was made available to the public.”

The practical problem therefore is that the larger the machinery involved the harder it is to design a test that cannot be seen to have potentially disclosed the invention. For inventors though this case demonstrate the importance of conducting tests in circumstances where it can be shown there is no prospect of being overlooked.


Hacon HHJ’s decision and application of the law make it very difficult to conduct large scale experiments, because by their nature they may need to be outdoors where technically they can be overlooked. This decision is therefore of great concern, as it establishes a genuine practical problem to experimentation of anything large. Many may consider it unfair for an inventor to be expected to consider the height of his garden hedge or the angle of view from an adjacent path before daring to test and evaluate his invention on private land. What is very clear is the screening to hide experiments needs to be in mind, as does confidentiality of those within your control who might otherwise see an experiment. It is clear (as it has always been) that inventors need to take special care to avoid making a public disclosure when evaluating and testing their invention, but it is not enough to assume that your testing location is private.

In the near term inventors should take extra practical care and perhaps engage advisors on how to contractually and practically secure a testing location to avoid later invalidation of their patent. More judicial focus on this question would be welcome, to ensure we have given proper consideration to the practical issues raised. It would assist if there was more focus on whether what can be seen is truly enabling so that mere observance of a machine in a field is no longer enough to invalidate a patent. Until such further determination though, inventors are advised to take the upmost caution when testing or evaluating their inventions outdoors.

A copy of the IPEC’s decision can be found here and a copy of the earlier Hozelock case can be found here.