Clarity, Scope & Context of Claims
If you file an application for a patent,and the patent office cites prior art which “anticipates” your invention, it means that the later invention (your invention) is merely an adaptation or variant of one or more earlier patents (the prior art), which would be obvious to a person skilled in the art (in the technical area or specialisation). This determination by an examiner may can be challenged in certain circumstances, but we advise that you first contact an IP professional to underake an assessment. Sanrixa has experienced Intellectual Property professionals trained in the UK who can help you consider and dissect such a determination.
In General Tire  RPC 457 at page 486, it was stated that to anticipate a patentee’s claim, a prior publication must contain clear and unmistakable directions to do what the patentee claims to have been invented. The prior inventor must be shown to have clearly planted his flag at the precise destination before the patentee.
Scope: the Limits of a Patentee’s claim & Infringement
The Patents Act 1977 9as amended) states in Section 125(1) that: …an invention for a patent for which an application has been made or for which a patent has been granted shall, unless the context otherwise requires, be taken to be that specified in a claim of the specification of the application or patent, as the case may be, as interpreted by the description and any drawings contained in that specification, and the extent of the protection conferred by a patent or application for a patent shall be determined accordingly.
In practice, this means the limits and scope of your invention is determined by your claims, with the drawings and description helping to explain those claims. The claims, read on their won must be clear and to define the invention, otherwise an objection may be raised by the patent authority, if there is something in the description which is inconsistent with the claim(s) or in some other way casts doubt on the true scope of the invention.
In past decisions the courts have adopted what is known as a “purposive construction of claims”, by giving effect to what would have been understood by the notional addressee, although these have been enriched by more recent case law. In the decision of Catnic Components Ltd and another v Hill and Smith Ltd  RPC 183, Lord Diplock stated (at page 243):- “A patent specification should be given a purposive construction rather than a purely literal one derived from applying to it the kind of meticulous verbal analysis in which lawyers are too often tempted by their training to indulge”. However in the Supreme Court in Warner-Lambert Company LLC v Generics (UK) Ltd (t.a. Mylan) & Anor.  UKSC 56 it was held that claims should be construed purposively in light of the description, and validating construction should not be applied to give claims a meaning which preserves their validity, if this is not the meaning that the skilled person would read into the claim. In Palmaz’s European Patents (UK) ( RPC 47, upheld on appeal  RPC 631) Pumfrey J held that words of degree such as “thin” must take their meaning from the context. Different meanings could not be attributed either to exclude acknowledged prior art or to be consistent with representations made by the patentee’s patent attorneys in a letter to a patent office. Similarly, in Hoechst Celanese Corp v BP Chemicals  FSR 319 the Court of Appeal held that there was no rebuttable presumption that words in a patent specification which could have a technical meaning did have that meaning.
In Actavis UK Limited and others v Eli Lilly and Company  UKSC, Lord Neuberger went on to consider two issues, each of which is to be considered through the eyes of the person skilled in the relevant art. Those issues are:
(i) does the variant infringe any of the claims as a matter of normal interpretation; and, if not, (ii) does the variant nonetheless infringe because it varies from the invention in a way or ways which is or are immaterial?
If the answer to either issue is “yes”, there is an infringement; otherwise, there is not. Such an approach complies with Article 2 of the Protocol, as issue (ii) squarely raises the principle of equivalents, but limits its ambit to those variants which contain immaterial variations from the invention. Issue (i) self-evidently raises a question of interpretation, whereas issue (ii) raises a question which would normally have to be answered by reference to the facts and expert evidence.
Article 69(1) of the European Patent Convention (EPC) (which corresponds to s.125(1) of the Patents Act) and The Protocol on the Interpretation of Article 69 of the EPC, are material in claim construction and the scope of protection afforded by a patent.
It was further held in Actavis that to conflate the two issues above as a single question of interpretation, as had been done by Lord Hoffman in Kirin-Amgen v Hoescht Marion Roussel Ltd  RPC 9, following his approach in Improver Corporation v Remington Consumer Products Ltd  FSR 181 (which itself had followed Lord Diplock’s analysis in Catnic) is wrong in principle, and can lead to error. Instead, issue (ii) involves not merely identifying what the words of a claim would mean in their context to the notional addressee, but also considering the extent if any to which the scope of protection afforded by the claim should extend beyond that meaning. With regard to issue (i), in Icescape Ltd v Ice-World International BV & Ors  EWCA Civ 2219, Kitchin LJ said “I have no doubt that…issue (i) involves purposive interpretation”. Therefore when considering infringement using issue (i), purposive interpretation must still be used.
In conclusion, the general principle is that the scope of a claim should to give fair protection for the patentee, but also a reasonable degree of certainty for third parties. In infringement, it means equivalents may be instructive, but must be interpreted in the correct context.
This is a summary of the subject which as you can see is very complex, but for more information and in-depth guidance, please refer to the source material (Manual of Patent Practice) here.