“23— (1) Liability to a penalty under any paragraph of this Schedule does not arise in relation to a failure to make a return if P satisfies HMRC or (on appeal) the First-tier Tribunal or Upper Tribunal that there is a reasonable excuse for the failure. (2) For the purposes of sub-paragraph (1)— …. (c) where P had a reasonable excuse for the failure but the excuse has ceased, P is to be treated as having continued to have the excuse if the failure is remedied without unreasonable delay after the excuse ceased.”
“… as a matter of policy such ignorance [of the law] cannot amount to a reasonable excuse. Ignorance of the law cannot be a reasonable excuse as that would result in the law favouring persons who choose to remain in ignorance of the law over those who sought to know the law in order to obey it.”