Catnic Components Ltd v Hill & Smith Ltd (No.1)
In this case, the plaintiffs were proprietors of a patent for steel lintels. The defendants copied and manufactured it. The defendants then produced a second form of lintel which differed slightly. The plaintiffs brought a second action in respect of this lintel, and further included a claim for breach of copyright.
The arguments involved consideration of (a) the construction of that claim; (b) the effect of the change of design from DH2 to DH4 and (c) the application of the doctrine of infringement by taking the “substance” or “the pith and marrow” of an invention to the facts of this case.
Held (House of Lords):
To determine whether a claim of a patent has been infringed one must first discover what is claimed. The claim must be construed and analysed to ascertain what are the features—sometimes called the integers—of the subject matter for which a monopoly is claimed. The claim must be construed in the context of the specification as a whole and in the light of any admissible evidence. It must be read and interpreted as it would be read and interpreted by the notional addressee of the specification, that is to say, a man skilled in the relevant art who has at his disposal the common knowledge in that art at the date of the publication of the specification. When so construed the claim must be analysed to discover what are the several features of the thing for which a monopoly is claimed. One must next consider the alleged infringement to determine whether it infringes the claim. If the alleged infringement of the claim has all the features of the claim it must infringe the claim, even if it also incorporates other features. If it lacks one of the features of the claim, it may or may not infringe the claim. If the feature which is lacking is an essential feature of the claim, there will be no infringement; but, if the feature which is lacking is an inessential feature of the claim, the fact that it is wholly omitted from the alleged infringement, or is replaced by some equivalent, will not save the alleged infringement from being an infringement, for, if it has all the essential features of the claim, it will infringe the claim notwithstanding the omission or substitution of an inessential feature.
A patent specification should thus be given a purposive construction and the specification must be read and interpreted as it would be by a man skilled in the art. A patent is infringed if it would be apparent to a reader skilled in the art that a descriptive word could not have been intended to exclude minor variants which would have no material effect upon the working of the invention. The House of Lords also concluded that no breach of copyright had occurred in this case.
 This case is also known as Catnic Components Ltd v Hills & Rutter; House of Lords; 27 November 1980
 lintels are beams placed over openings, for example, doors or windows, to support courses of building material above the openings or, possibly, roof trusses.
 At p.28; This formulation states the effect of the views expressed by the House of Lords in Rodi and Wienenberger A. G. v. Henry Showell Ltd.  R.P.C. 367. In several cases in which infringement by taking the “substance” or “pith and marrow” of a patentee’s invention has been discussed, this doctrine has been referred to as a protection against colourable evasion of infringement.