Patents bestow upon their owners powerful monopolistic rights, entitling them to control the use of their inventions for a finite period. Although monopolies are generally regarded as being contrary to the public interest, an exception is made in the case of patents because there is perceived to be a 'bargain' whereby the grant of exclusivity is assumed to encourage the disclosure by patentees of their inventions, thereby adding to the pool of human knowledge such that the inventions will then become available for use by all at the expiry of the patent term (usually 20 years)[1].

In order to demonstrate that an invention is a true contribution to the prior art over what was known before, it must satisfy the requirements of novelty, obviousness and sufficiency. These tests are set against what would have been already known and understood by "a person skilled in the art"[2] – a notional individual or team who is skilled in the area but who is treated as lacking any imagination or ingenuity and, thus, a fictitious character. Within the assessment exercise, this legal fiction is continued in that the skilled person is also deemed to have read every document that would have been available at the priority date, even if in reality this would have been unlikely the case (the "Deemed Read Rule").

The difficulties of assessing what is obvious over the prior art, as well as the possible harsh consequences of the Deemed Read Rule, have been debated recently before the Court of Appeal in a dispute involving patent rights granted in relation a new type of garden hose[3]. By way of a majority verdict, the Court held that the patents underpinning the inventive hose were invalid for reasons of obviousness over an earlier application published eight years before the priority date. All the three judges were in praise of the hosepipe devised by the inventor. Nevertheless, despite acknowledging his ingenuity, the Court held that the principles supporting the bargain, between the state and the inventor, outweighed their admiration for his invention. For the state/inventor bargain to remain robust, the rule that the skilled person is deemed to have read all prior documents – no matter how obscure they might be – must be upheld. 

The complexity in applying the test of obviousness especially where the prior disclosure is only contained in a paper, which has not been further revealed by being put into practice, was brought into stark relief when it is recalled that in a previous dispute involving one of the very same patents and very same prior art (but with different defendants, different expert evidence about the attributes of the skilled person as well as different legal teams), both the High Court and the Court of Appeal in Blue Gentian LLC & Or v Tristar Products (UK) Limited & Or ("Blue Gentian")[4] had reached an opposite conclusion and had found that the patents were not lacking inventive step, but were valid and infringed.


The patents in dispute, UK Patent No 2 490 276 ("UK '276") and European Patent (UK) No 2 657 585 ("EP '585"), are titled "Expandable Hose Assembly", have a priority date of 2011 (collectively, the "Patents") and relate to a hosepipe which expands under water pressure but which is compact when relaxed. The claimant/appellant, E.Mishan & Sons Inc, which trades as "Emson", is an exclusive sub-licensee under the Patents[5]. Emson had issued proceedings against Hozelock Ltd for the sale of its expandable hose known as the SUPERHOZE. Hozelock denied infringement and counterclaimed that, inter alia, the Patents were invalid for being obvious over a US patent application No. 2003/000530 ("McDonald").

The Patents specify a hose with an inner tube (usually of rubber) inside an outer tube (usually of a non-elastic, relatively soft fabric, such as woven nylon). The outer tube is secured to the inner tube only at the ends and, when the hose is connected to a pressurised water supply such as a water tap, it will expand longitudinally up to six times its length. Radial expansion is constrained by the outer sheath. On release of the pressurised water, the inner tube will contract and cause the outer tube also to retract. Figures 9 and 5 and figures 10 and 6 of UK '276 show the invention in its contracted state and in its expanded states.

IP - 1

Sold by Emson under the XHOSE brand, this expandable pipe has enjoyed substantial commercial success and represented a radical departure from previous garden hose pipe designs. This success was achieved through what Henderson LJ (one of the two judges who found against the patentee) described as a "brilliantly simple invention". Lord Justice Floyd, the dissenting judge, who conversely held that the Patents were valid described the invention as one of "breathtaking ingenuity bringing with it real practical advantages over what was available" [paragraph 86]. 

The key advantages of the invention, as specified in the Patents and promoted on the packaging of the XHOSE, are that it is:

  • expandable, thus allowing for space saving when stored
  • much lighter than other garden hoses; and
  • flexible and retractable, so as to prevent kinking or entanglement (a problem prevelant in more rigid hosepipe designs when being stored).

McDonald: the prior art

McDonald proceeded to grant in the USA and in Europe (UK, FR, DE) but there is no evidence that it had ever been commercialised or otherwise put into practice. It is titled "Self elongating oxygen hose for stowable aviation oxygen mask" and is intended for use in an aircraft's pilot cabin as a supplementary breathing apparatus for the quick delivery of oxygen to the crew in the event of an emergency. The abstract of McDonald describes:

"the assembly (14) is designed so that when the mask (12) is pulled from the box (16), pressurized gas passing through the hose assembly (14) serves to inflate and axially expand the assembly (14) to a deployed length greater than the relaxed length thereof. The assembly (14) preferably includes an inflatable elastomeric inner tube (30) together with an exterior sheath (36) of woven or braided material which restricts radial expansion of the tube (30) while permitting axial expansion thereof. In preferred forms, the deployed length of the assembly (14) is up to three times greater than the relaxed length thereof."

The two figures that relate to the specification of McDonald, showing its expanded and contracted states are below.

IP - 2

Accordingly, McDonald is a document describing the invention as a hose that is self-elongating. McDonald's abstract then explains that through pressurised gas, the hose, comprising an outer tube and an inner tube, will permit expansion up to three times greater than its relaxed length (axially but not radially) – in a manner as suggested later by the Patents. McDonald gave the ease of storage in the cramped conditions of an aircraft's flight deck as an advantage of the invention.

Earlier in Blue Gentian, Mr Justice Birss had ruled (in a decision upheld in the Court of Appeal) that the unimaginative skilled person working without hindsight (which is not permitted when assessing obviousness – see Pozzoli [6]) would not apply the principle of McDonald to garden hoses. He held that, if presented with McDonald, the skilled but unimaginative garden water hose designer would have decided that this was a document which was not addressed to them. Moreover, Mr Justice Birss was conscious that McDonald was only a paper document and he noted that the claimant's expert had questioned how effectively McDonald would have worked in practice. For example, there was a query whether the McDonald invention might have got tangled up if it expanded whilst still inside the box. The judge also concluded that McDonald did not clearly explain how the breathing tube would deploy and retract. Accordingly, although the skilled unimaginative person would be deemed to have read McDonald, it was held that such person would not have believed it to be a document addressed to them.

The High Court decision

Subsequently, in this case brought against Hozelock before Mr Justice Nugee[7], there have been different findings reached from the expert evidence – most significantly, that the notional skilled person engaged in the design and manufacture of garden hoses (although not aware of expandable garden hoses prior to the XHOSE) would have (i) had knowledge about technical hoses; (ii) understood the principle upon which McDonald was based; (iii) known that hoses can have various applications; and (iv) seen both gases and water as fluids. In Blue Gentian, neither party brought forward any experts who had experience in the design and manufacture of hoses, relying instead on those experienced in either in the manufacture of plastic products or the use of polymers.

Mr Justice Nugee ruled that the Patents were invalid for lack of inventive step over McDonald but, save for such invalidity, the SUPERHOZE would have infringed at least the main claim of the Patents. In answer to the fourth Pozzoli question – whether, viewed without any knowledge of the alleged invention as claimed in the Patents, the differences with McDonald constitute steps which would have been obvious to the person skilled in the art or they require any degree of invention – Mr Justice Nugee held that any differences would have constituted steps which would have been obvious.

The Court of Appeal decision

Emson appealed on the grounds that the High Court judgment failed to give appropriate weight to the huge commercial success enjoyed by the XHOSE, and that it was based ex post facto on hindsight.

Commercial success

Lord Justice Floyd, in his dissenting judgment, agreed with Arnold LJ that the commercial success of the invention could not assist Emson to defeat the attack of obviousness over McDonald, because there was no evidence that McDonald was known to anyone in the hose industry. Accordingly, it could not be argued that the fact that such a device was not produced soon after the publication of McDonald – bearing in mind how great its success – the XHOSE was not obvious over McDonald [see paragraphs 78 and 86].


At paragraph 56, Arnold LJ stated that "For the purposes of the obviousness enquiry, the skilled person is deemed to be interested in solving the problems of space, weight and kinking with conventional garden hoses. The skilled person is then deemed to read McDonald, but without any preconception that it will assist him to solve any of those problems. The question is whether it would then be obvious to adopt the principles of McDonald's hose for a garden hose. The judge was entirely correct to say that the skilled person is not deemed to be engaged in making an oxygen mask assembly." 

Lord Justice Arnold did not accept that this case gave rise to the type of 'mindset issue' as was considered in Dyson v Hoover [2001] RPC 27, where "no-one would think of dispensing with a bag, and the skilled person would approach the suggestion of using cyclonic action instead with reserve if not scepticism" [paragraph 49]. In the circumstances, there was nothing to suggest that the skilled person would conclude that McDonald could not be adapted for use as a garden hose. The lack of information in McDonald about gas pressures, the retraction of the hose retracts, and the diameter sizes of the hoses, would not deter the skilled person from considering applying McDonald to garden hose technology – a field in which innovation was rife. Also, the need to consider working with unfamiliar materials would not deter the skilled person. In the view of the majority of the Court of Appeal, this lack of detail would not be a factor causing the skilled person to put aside McDonald as being too confusing.

McDonald spoke of the need for space saving, even if it was silent on the other advantages of the XHOSE (i.e. light-weight and no kinking). The allegation of obviousness did not require a step by step analysis; "it only requires a single step to get from McDonald to the claimed invention. Moreover, McDonald's hose is as simple in conception as the hose described and claimed in the Patents" [paragraph 75].

Lord Justice Arnold had sympathy for the inventor but commented that, in the application of the Deemed Read Rule, "when attacking the validity of a patent, the party doing so is allowed to select the prior art used as the foundation for the argument with 20/20 hindsight. To that extent (but only to that extent), hindsight is not merely permitted, but an inherent feature of the current design of the European patent system (and indeed, of most patent systems worldwide). It inevitably follows that some patents turn out to be invalid because, unbeknownst to the inventor, or indeed other persons skilled in the relevant art, prior art emerges when sufficient searches are carried out which anticipates or renders obvious the claimed invention. The judge concluded that this was such a case so far as obviousness over McDonald was concerned, and I see no basis on which this Court is entitled to interfere with that conclusion".

Lord Justice Henderson also expressed sympathy for the inventor but concluded at paragraph 85 that McDonald could not be overcome as prior art because it "unambiguously disclosed the same basic concept of an extensible and retractable hose as Mr Berardi's later invention. That concept was clearly expressed, both verbally and visually, in the original patent application for McDonald. Bearing in mind that the notional skilled person was a designer of hoses in general, not just of garden hoses, and that he was familiar with the transposition of a hose structure from one application to another (see the judgment at [177]), it seems to me only a small step, and not an impermissible exercise in hindsight, to conclude that the skilled person would at once have seen the potential for use of the same basic idea in the construction of a garden hose. The question of how to make the idea work in practice would not then have been a problem, because as every gardener knows the operation of a garden hose depends on nothing more sophisticated than its attachment at one end to a pressurised supply of water through an ordinary household tap".

In his dissenting judgment, having acknowledged the Deemed Read Rule can be harsh, Floyd LJ pointed out that such harshness can be mitigated in two key respects:

  • the notional skilled person is not assumed to know or suspect that the prior art has the answer for the problem that is faced; and
  • 'mere paper proposals', in particular unworked proposals in patent specifications such as McDonald, should be treated with particular care. 

Lord Justice Floyd also warned that "Hindsight is a particular danger where the invention is a simple one" [paragraph 96]. Steps from the prior art to the invention can look seductively simple when one knows the direction in which "the telescope is pointing" [paragraph 98].

Lord Justice Floyd concluded that Mr Justice Nugee's judgment was redolent with hindsight caused largely by him having treated McDonald not as just a mere paper proposal, but instead as a working machine. This approach had caused the judge to be unduly dismissive of the concerns of Emson's expert about the practicalities behind McDonald if such had been implemented. This also led the judge not to be sufficiently sceptical as to how McDonald would have worked in practice, e.g. it had been unclear on the evidence as to the means by which the McDonald tube would have retracted [paragraph 109]: "There is all the difference, however, between transposing a hose structure shown to have worked well in the different field, and transposing a mere paper proposal from that field" [paragraph 110].

In the view of Floyd LJ, Mr Justice Nugee had focused overly on space saving – just one of three advantages that XHOSE brought to the state of the art (the others being lightness of weight, and no kinking). Space saving was a characteristic which only with hindsight did, in the judge's mind, take on a far greater significance than it deserved. The judge should have taken into account how the design of garden hoses had not materially changed for decades up to the introduction of the XHOSE in 2011. Even accepting that the notional person would have had exposure to technical hoses such as McDonald and even accepting that this might be a 'mindset' scenario albeit less stark than the 'dust bag vs cyclonic technology' debate which featured in Dyson v Hoover (ibid) "the idea that the notional, unimaginative skilled person with an interest in this industry would seize on an untested proposal from a 'very particular and very distant field' has the air of unreality when no ideas (even practical ones) appear to have been so transposed for so long". In his view the judge should not have dismissed out of hand the 'mindset' arguments of Emson's counsel, or those based upon how the skilled person would have to work with unfamiliar materials if McDonald was transposed into the field of garden hoses. Lord Justice Floyd said that the key question was what would have made the skilled person see a connection between McDonald and garden hoses.

He concluded that "Viewed with the principles I have mentioned in mind, there is nothing in McDonald to suggest the idea of an expandable garden hose, let alone the combination of advantages which Mr Berardi's invention brings…I would have allowed this appeal" [paragraph 120].


The decision is a reminder how, when assessing obviousness, there is often a great difference between the skilled person reading a document and their understanding and appreciation of such. Moreover, the conflicting earlier judgment in Blue Gentian shows how crucial in infringement and validity disputes, is the choice of expert witnesses to opine on the background and context to the invention. Since the Deemed Read Rule is a cornerstone to patent law, it is understandable why the majority of the Court of Appeal found the Patents in this case to be invalid over McDonald; however, the dissenting judgment of Floyd LJ is a warning about reading too much from a mere paper proposal.


[1] Lord Briggs in Regeneron Pharmaceuticals Inc v Kymab Ltd [2020] UKSC 27 at paragraph 23

[2] Section 3 of the Patents Act 1977

[3]E. Mishan & Sons, Inc. v Hozelock Ltd & Ors [2020] EWCA Civ 871, 8 July 2020

[4] [2013] EWHC 4098 & [2015] EWCA Civ 746

[5] EP '585 is owned by Blue Gentian LLC and UK '276 is owned by Telebrands Corp, respectively the second and third respondents. Although respondents to the appeal, they did not participate in the proceedings.

[6]Pozzoli SpA v BDMO SA [2007] EWCA Civ 588

[7] [2019] EWHC 991