Section 239 | Reasonable excuse
From legislation.gov.uk
(1)A person is not liable to a penalty under section 234, 235 or 238 if the person satisfies an authorised officer of Revenue and Customs or, on an appeal to the tribunal, the tribunal that there is a reasonable excuse for the contravention.
(2)If a person had a reasonable excuse for a contravention but the excuse has ceased, the person is to be treated as having continued to have the excuse if the contravention is remedied without unreasonable delay after the excuse ceased.