Here Lord Neuberger explains at paragraphs 19 to 25, for the benefit of all, what might be called the Modern Law of Undertakings (citations omitted):
On the facts the Court of Appeal, allowing the appeal, held that no undertaking had been given. with luck, if the court's words are heeded, this issue will never need to trouble any judge in patent proceedings again.
"An undertaking is a very serious matter with potentially very serious consequences. It is a solemn promise to the court, breach of which can lead to imprisonment or a heavy fine. Accordingly, there should never be room for argument as to whether or not an undertaking has been given. Further, while there is inevitably sometimes room for argument as to the interpretation of an undertaking, the circumstances in which such arguments can be raised should be kept to a minimum. Accordingly, any undertaking should be expressed in full and clear terms and should also be recorded in writing.
None of this is either controversial or original. Unsurprisingly, it is well established. ... "it is in all cases highly desirable that any undertaking to the court shall be recorded and served on the giver personally". ... the "most obvious and convenient way … is to record the undertaking in an order of the court …". ... "the general practice to be adopted" was that the "undertaking should be included in a recital or preamble in the order of the court", which should be issued and served on the person who gave the undertaking with a penal notice. ...
... in a case where there is a bona fide dispute as to whether an undertaking has been given, the fact that neither the existence nor the terms of the undertaking has been recorded in writing militates against an undertaking having been given. All the more so where the court has made an order in which the undertaking, if given, could and should have been recorded. ... in a case where an undertaking has been given, even where the court makes no order, that ought itself be recorded in a formal order which should recite in full any undertaking that has been given.
... it must also follow ... that, where the terms of an undertaking could equally well be interpreted as having a narrow scope or a wide scope, it is the narrower scope which must prevail. An accusation that there has been a breach of an undertaking has similarities with an allegation of criminal behaviour, and it therefore must be right that, where two interpretations of an undertaking are equally convincing, the less stringent one should prevail. (Of course, in some circumstances, the terms of an undertaking may be ambiguous in such a way as to render the undertaking simply unenforceable).
In this case, the undertaking is said to have been given orally, and was never committed to writing (save that the variation to the patent which would have resulted from the alleged undertaking was written down and handed to the court). The argument as to whether an undertaking was given, and what its terms were, has therefore centred on the transcript of what was said at the hearing. Quite apart from the self-evident undesirability of courts having to trawl through transcripts of earlier hearings to consider whether any binding commitments were made on behalf of any party, and, if so, the meaning and extent of any commitment, there are, I think, four points of principle to bear in mind when considering transcripts in such circumstances.
First, all the relevant passages must be read together and, of course, in their overall context. Secondly, one should be wary of indulging in what Lord Diplock characterised as "detailed semantic analysis" of the words revealed by the transcript: if such analysis can be inappropriate in relation to formal written contracts, it must be a fortiori when it comes to oral exchanges in court. Thirdly, if there is real doubt as to the meaning or effect of what was said, it should, as mentioned, be resolved in favour of the person who would be bound. Fourthly, it is permissible to have regard to what was said and done after the undertaking is said to have been given, in order to assist in resolving whether it was, and, if so, what its terms were ....
... The fact that undertakings should be recorded formally in writing in clear terms does not mean that the court is bound to conclude that, where that has not happened, no undertaking has been given. There is no rule that an undertaking given to the court must be recorded in writing before it can be effective. In other words, whether an undertaking has been given is ultimately a question of fact in each case. Equally, the fact that, in cases of doubt, an undertaking should be construed beneficially to the person who gave it, does not mean that the court should search for uncertainties or ambiguities in undertakings. Ultimately, an undertaking is to be interpreted in the same way as any other document (assuming that it is in documentary form, as it ought to be)".