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IPEC finds patent invalid on the grounds of prior use by inventor

Posted on 10 May 2021

A recent judgment in the Intellectual Property Enterprise Court (IPEC) has developed the law relating to the circumstances in which prior use of an invention may invalidate a patent, following 2019's Mishan v Hozelock decision. The IPEC's decision in Claydon Yield-O-Meter v Mzuri has made clear that, in circumstances where the defence to a prior disclosure is that the inventor would pack up their invention and walk away if being watched, the burden is on the patentee to show not only that they would have done so, but also that it was possible to do so in the circumstances. When assessing whether prior use has made an invention available to the public, it does not matter that nobody took advantage of that availability – the information made available is that which would have been noticed or inferred by a person skilled in the art who, hypothetically, would have taken advantage of access to the invention.


In Mishan v Hozelock, a case relating to the invention of expandable garden hoses, the inventor had developed his invention by conducting and documenting experiments in his garden. As certain parts of the garden were visible from the public road, the Defendants argued that this constituted an enabling disclosure through prior use; although no-one in fact viewed the experiments, they were in theory free to do so. The patentee's answer to this was simple: if someone was watching him from the road, he would have packed up his equipment and moved out of sight of the road to the back of his house. On the facts of that case, the judge accepted that he would have, and could have, done just that. As a result, in that case there was no enabling disclosure (albeit the patent was found invalid on other grounds).

In Claydon Yield-O-Meter v Mzuri, a case relating to a piece of agricultural machinery – a device pulled by a tractor which drilled holes in the soil in which to plant seeds –  the patentee sought to rely on similar arguments. The IPEC found that, had the patent been valid, it would have been infringed by the Defendant's machinery. A separate patent was not valid and was not infringed.

Prior use in Claydon v Mzuri

The relevant facts are similar to those in Mishan v Hozelock. Prior to the priority date of the patent, the inventor, Mr Claydon, alongside his brother, tested a prototype version of the machinery in a field on his farm over two days. The field was visible from nearby roads and from a public footpath. Mr Claydon argued that not only was no-one ever present on the footpath when they were testing the prototype, but further that he and his brother had discussed what to do if anyone else was present – they would have moved away so that no-one could see any relevant detail.

However, in this case, the judge found that the prototype was made available to the public, and therefore the patent lacked novelty because of the prior use.

There were several distinctions from Mishan v Hozelock which led to this decision:

  1. Mr Claydon's evidence regarding the exact steps he would have taken (some 20 years earlier) were not consistent under cross-examination compared to his witness statement.
  2. In any event, it was significantly more difficult to take steps to hide a large piece of agricultural machinery placed in the middle of a field than it was to hide a garden hose.
  3. There was evidence that the prototype would have left patterns in the soil from which it could be deduced how the invention worked (the soil would have alternate lines of tilled and untilled soil, and therefore it would be clear that the two rows of tines would be aligned.) It was not clear how Mr Claydon could have taken action to prevent a skilled person from viewing that evidence if they happened to be on the footpath.

Use of technical equipment

The Defendants unsuccessfully argued that the hypothetical skilled person observing would have had the benefit of binoculars or a video camera. Whilst the judge suggested there was no absolute bar to enablement of an invention where the hypothetical skilled person would gain an understanding of it through using technical equipment, he identified some potential difficulties in practice.

In any event, the judge did not consider that there was enough evidence on what equipment a member of the public might have been carrying and have used to observe the prototype, without being in breach of an implied obligation of confidence. As a result, the decision was based on what could have been seen with the naked eye. A modern camera phone would reveal far more than the naked eye, and the door has been left open for defendants in the future to argue that a skilled person would have and use such a device in these circumstances.

Practical tips

The court in both cases focused on the likely steps the inventor would take if and when they would have become aware of being observed by a hypothetical observer, and the effect it would have had on the skilled person's ability to gain information.  Practically, therefore, where it is not possible to test a prototype privately or under conditions of confidentiality, inventors need to continue to be mindful of whether a skilled person could hypothetically be viewing a prototype being developed. Inventors seeking to rely on the arguments relied upon in Hozelock should ensure firstly they have clear, preferably contemporaneous, evidence as to what they would have done if a skilled person had appeared and started to view any potential enabling disclosure; and secondly that they have the ability not only to properly conceal any prototype product, but also any evidence of its use.

Defendants, meanwhile, should consider adducing evidence of what technical equipment a hypothetical skilled person might have had and used in the specific circumstances.

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