"The element of guess-work and the almost unavoidable inaccuracy in a properly made best of judgment assessment, as the cases have established, do not serve to displace the validity of the assessments, which are prima facie right and remain right until the taxpayer shows that they are wrong and also shows positively what corrections should be made in order to make the assessments right or more nearly right." ( Bi-Flex Caribbean Ltd v Board of Inland Revenue (1990) 63 TC 515, 522-3 PC per Lord Lowry). That was confirmed by this court, after a detailed review of the authorities, in Customs and Excise Commissioners v Pegasus Birds Ltd[2004] STC 1509 ; [ 2004] EWCA Civ 1015 . We also cautioned against allowing such an appeal routinely to become an investigation of the bona fides or rationality of the "best of judgment" assessment made by Customs: "
“ Well, what does ‘evasion’ mean? Evasion is an English word that means to get out of something. If you evade something, you get out of its way, you dodge it … What is dishonesty in English Law? It is a common English word and it carries its ordinary English meaning. You [the Jury] must decide for yourselves, first of all, whether ordinary, right-thinking people would describe what Mr. Dealy did as dishonest. If the answer is “No, ordinary, sensible people would not regard what he did as being dishonest” then he is not guilty. However, if you decide that ordinary, reasonable people would see his conduct as dishonest, you must then go on to decide what he thought about it. If you come to the conclusion that Mr. Dealy might have thought, quite honestly, that he had a perfect right to do as he did, and that no-one would regard it as dishonest, then he is not guilty. If he was convinced, throughout, that he was doing the right thing, and that other people would agree with him, that is not dishonesty.””
“… the fact that suppression of takings took place on a scale that Mr Rahman must have been aware of, and on the basis of the whole of the evidence presented to us, as we have already found, it was he who suppressed the takings, we are satisfied to the high degree of probability required that he dishonestly evaded the tax we have determined to be due.”