“In such cases….. 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 if it 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”. (2) Pegasus Birds Carnwath LJ (now Senior President, The Appeals Service) in the lead judgment stated: “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. Where the taxpayer seeks to challenge the assessment as a whole on “best of their judgment” grounds, it is essential that the grounds are clearly and fully stated before the hearing begins. In particular the Tribunal should insist at the outset that any allegation of dishonesty or other wrongdoing against those acting for the Commissioners should be stated unequivocally; that the allegation and the basis for it should be fully particularised; and that it is responded to in writing by the Commissioners. The Tribunal should not in any circumstances allow cross-examination of the Customs officers concerned, until that is done. There may be a few cases where a “best of their judgment” challenge can be dealt with shortly as a preliminary issue. However, unless it is clear that time will be saved thereby, the better course is likely to be to allow the hearing to proceed on the issue of amount, and leave any submissions on failure of best of their judgment and its consequences, to be dealt with at the end of the hearing”