SolvedECP2700 | General principles: Reasonable excuse
From HM Revenue & Customs · Excise Civil Penalties Manual
Most excise civil penalties are subject to the reasonable excuse provision contained in Section 10 of the Finance Act 1994.
Where a person has a reasonable excuse for the conduct which caused the breach, for example, short term illness or sudden death of personnel with key roles relating to the breach, or computer failure at a critical time, there is no liability to a penalty.
Guidance on reasonable excuse can be found at ECP8000.