“ Clearly [HMRC] must perform that function [of exercising their powers in such a way that they make a value judgment on the material which is before them] honestly and bona fide. It would be a misuse of that power if the commissioners were to decide on a figure which they knew was, or thought was, in excess of the amount which could possibly be payable, and then leave it to the taxpayer to seek, on appeal, to reduce that assessment .” 64. In the later case of in Rahman (t/a Khayam Restaurant) v CEC[1998] STC 826 Carnwath J expanded on this. He noted that a two stage approach is required as follows (at page 876) "… the practice is to consider these cases in two stages: (1) consideration whether the assessment was made according to the "best judgment of the Commissioners"; if not, the assessment fails, and stage (2) does not arise; (2) if the assessment survives stage (1), consideration whether the amount of the assessment should be reduced by reference to further evidence or further argument available to the Tribunal…" 65. He then commented on the approach taken by Woolf J in the Van Boeckel case as regards the first “best judgment” stage cautioning that the tribunal should not find that an assessment was invalid purely because it disagrees as to how judgment should have been exercised but that a much stronger finding is required: “… for example, that the assessment had been reached “dishonestly or vindictively or capriciously”; or is “spurious estimate or guess in which all elements of judgment are missing”; or is “wholly unreasonable”” 66. He went on to say that, if he was right in his interpretation of Van Boeckel , it is only in a very exceptional case that an assessment will be upset because of a failure by the Commissioners to exercise “best judgment”
"In such cases - of which the present is one - the relevant question is whether the mistake is consistent with an honest and genuine attempt to make a reasoned assessment of the VAT payable; or is of such a nature that it compels the conclusion that no officer seeking to exercise best judgment could have made it. Or there may be no explanation; in which case the proper inference may be that the assessment was indeed arbitrary . " 69. Chadwick LJ continued (at [43]) to give examples of cases where it may be apparent that the power to assess has not been exercised in accordance with “best judgment”, such as where the Commissioners have not taken into account information which was made available to them by the taxpayer before the assessment was made, or can put forward no basis upon which the assessment can be supported. He said that he “suspected that those cases will be rare”. At [44] he noted that in the usual case the tribunal “will have the material before it from which it can see why the Commissioners made the assessment which they did; and may have further material which was not available to the Commissioners when the assessment was made”. In such cases “a tribunal would be well advised to concentrate on the question "what amount of tax is properly due from the taxpayer?"; taking the material before it as a whole and applying its own judgment. . . ." 70. He concluded at [45] that where there is a finding that “best judgment” has not been exercised, the tribunal could take the view that “the proper course is to discharge the assessment”. But even in cases of that nature “the tribunal could choose to give a direction specifying the correct amount….The underlying purpose of the legislative provisions is to ensure that the taxable person accounts for the correct amount of tax."
“The Tribunal should remember that its primary task is to find the correct amount of tax, so far as possible on the material properly available to it, the burden resting on the taxpayer. In all but very exceptional cases, that should be the focus of the hearing, and the Tribunal should not allow it to be diverted into an attack on the Commissioners' exercise of judgment at the time of the assessment.”
“ All that can be said is that an assessment may be so far outside the bounds of what would have been reasonable that it calls into question whether there was, indeed, an honest and genuine attempt to assess the amount properly due......But that is an evidential inference from the facts; it is not a finding that because (although doing his honest best) his assessment fell below an objective standard of reasonableness, he failed to exercise the power to assess to the best of his judgment as a matter of law. ”