City Technology Ltd v Alphasense Ltd

Patent claims must be construed in accordance with the Protocol on Interpretation of Article 69 EPC, balancing fair protection for the patentee with reasonable certainty for third parties. A variant may infringe where it has no material effect on how the invention works, its equivalence would have been obvious to the skilled reader, and the claim does not indicate that strict literal compliance is essential.

Obviousness is assessed without hindsight by identifying the inventive concept, determining the skilled person’s common general knowledge, identifying the differences from the prior art, and asking whether those differences required invention.

City Technology Limited’s patent for a compact electrochemical gas sensor was held valid and infringed by the High Court, where Mr David Young QC sat as a deputy judge. Alphasense Limited appealed, arguing that its sensor fell outside claim 1 and that the patent was obvious in light of US patent 3 755 125 (Shaw) and common general knowledge.

The appeal concerned the construction of the claimed wick and separator arrangement and whether the claimed combination involved an inventive step.

1. Infringement. The Protocol on Interpretation of Article 69 EPC governed construction. The court applied the three questions stated in Improver Corporation v Remington Consumer Products [1990] FSR 181. The variant had no material effect on the operation of the invention, and its operation would have been obvious to the skilled reader.
2. The specification and claim did not indicate that a unitary wick extending continuously from the reservoir through the counter-electrode was an essential requirement. The claim was concerned with the hydrophilic wick arrangement conveying electrolyte to the separators, rather than with a strict distinction between a wick and a separator. The respondent’s sensor therefore infringed claim 1.
3. Validity. The court applied the four-stage approach in Windsurfing International Inc v Tabur Marine (G-B) Ltd [1985] RPC 59: identify the inventive concept; assume the mantle of the normally skilled but unimaginative addressee; identify the differences from the state of the art; and determine whether those differences were obvious.
4. The relevant common general knowledge was not established merely by showing that a matter was well-known. Following Wheatley v Drillsafe [2001] RPC 133, the evidence had to show that the matter formed part of the skilled person’s common general knowledge. The evidence did not establish that holes in electrodes, or the claimed use of them, formed part of that knowledge.
5. The redesign of Shaw required several coordinated changes, including replacing its electrode and wick arrangement and routing a wick through the counter-electrode. The proposed route to the invention depended on hindsight and ex post facto analysis. Neither Shaw nor common general knowledge made claim 1 obvious.
6. The appeal was dismissed. The patent was valid and infringed. By consent, Alphasense was ordered to pay City Technology’s agreed appeal costs of £37,500.

• High Court, Chancery Division: Mr David Young QC, sitting as a deputy judge, held the patent valid and infringed and granted relief.
• Court of Appeal (Civil Division): The appeal was dismissed. The High Court judgment was upheld.