In HMRC v Lansdowne Partners Limited Partnership [2011] EWCA Civ 1578 the taxpayer partnership (LPLP) lost the substantive issues in the case leaving the final issue as to whether HMRC's discovery amendment to LPLP’s partnership return was valid. The amendment was made under TMA 1970 s 30B(1) (the equivalent provision for individuals is s 29) on 27 August 2008. It was common ground that the enquiry window ended on 31 January 2007 and that HMRC ‘discovered’ that the profits in LPLP’s partnership statement were insufficient on 1 May 2008. The question was whether HMRC satisfied the condition in s 30B(6) that at the end of the enquiry window a hypothetical HMRC officer ‘could not have been reasonably...