"the tribunal should not treat an assessment as invalid merely because it disagrees as to how the judgment should have been exercised. 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'. In substance those tests are indistinguishable from the familiar Wednesbury principles (see Associated Provincial Picture Houses Ltd v Wednesbury Corp[1948] 1 KB 223 ). Short of such finding, there is no justification for setting aside the assessment."
"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."