"Where a person has failed … to keep any documents and afford the facilities necessary to verify such returns or where it appears to the Commissioners that such returns are incomplete or incorrect, they may assess the amount of VAT due from him to the best of their judgment and notify it to him."
“[69] There is no problem so far as concerns the appeal against the VAT assessment. The position on an appeal against a 'best of judgment' assessment is well-established. The burden lies on the taxpayer to establish the correct amount of tax due: '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 (See Bi-Flex Caribbean Ltd v The Board of Inland Revenue (1990) 63 TC 515 at 522–523 per Lord Lowry).’ That was confirmed by this court, after a detailed review of the authorities, in Pegasus Birds Ltd[2004] EWCA Civ 1015 ,[2004] STC 1509 . We also cautioned (see[2004] STC 1509 at [38]) 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: 'Evidence to the tribunal [38] ... (i) 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 ...'”