"I can see no reason for saying that a discovery of undercharge can only arise where a new fact has been discovered. The words are apt to include any case in which for any reason it newly appears that the taxpayer has been undercharged and the context supports rather than detracts from this interpretation."
"Mr Shelbourne said that "discovery" means finding out something new about the facts. It does not mean a change of mind about the law. He said that everyone is presumed to know the law, even an inspector of taxes. I am afraid I cannot agree with Mr Shelbourne about this. It is a mistake to say that everyone is presumed to know the law. The true proposition is that no one is to be excused from doing his duty by pleading that he did not know the law. Every lawyer who, in his researches in the books, finds out that he was mistaken about the law, makes a discovery. So also does an inspector of taxes." 27. Therefore, the fact that Mr Thackeray may have had sufficient evidence to reach a conclusion that there was an insufficiency of tax sooner than he did, does not, in our judgment, preclude him from reaching that conclusion and making a discovery at a later date. 28. Although we were referred to the decision of the House of Lords in Scorer v Olin Energy Systems Ltd[1985] AC 645 as authority for the proposition that the re-visiting of old facts cannot amount to a discovery we note that the issue in that case was whether an agreement, under s 54 TMA, by the Inspector to the taxpayer’s computation claiming a deductible loss precluded HMRC from raising a subsequent discovery assessment when they changed their mind about the correct tax treatment of the loss. 29. We agree with, and adopt, the comments of Lewison LJ in Hankinson , in relation to Scorer v Olin Energy , where he said, at [32-33]: [32] “Thus the question [in that case] concerned the scope of the agreement. That in turn was in effect a question of construction. Lord Keith of Kinkel (who gave the leading speech) made two points. First he said that the material presented in the taxpayer's computation "was sufficient to bring home to the mind of an ordinarily competent inspector in his position precisely what they were claiming"
"The situation must be viewed objectively, from the point of view of whether the inspector's agreement to the relevant computation, having regard to the surrounding circumstances including all the material known to be in his possession, was such as to lead a reasonable man to the conclusion that he had decided to admit the claim which had been made."