This was an appeal to the Upper Tribunal in which Patrick Cannon appeared for the taxpayers. The appeal concerned whether a hypothetical officer of HMRC could reasonably have been expected to have been aware that the self-assessment to tax was insufficient based on the information made available when the enquiry window closed. The decision has some useful comments at  and  about what the judges described later on as a “collateral attack” on the facts as found by the First-tier Tribunal.
In particular, the UT drew attention to what the Court of Appeal has said in FAGE UK ltd v Chabani UK Ltd  EWCA Civ 15 and Proctor & Gamble UK Ltd v HMRC  EWCA 407 about not interfering with the facts as found by the lower tribunal or with the evaluation of those facts and the inferences to be drawn from them. This creates a high threshold for taxpayers seeking to appeal to the UT in fact-sensitive tax cases.
Read the full decision here