EM5155 | Penalties: Culpability - Defences: Failure to Notify
From HM Revenue & Customs · Enquiry Manual
A taxpayer may claim that they did not notify HMRC because
they did not know there was an obligation to notify HMRC (or for 1988-89 to 1994-95 they did not realise that it was necessary to specify each separate source) EM5156
they did not know that their income was sufficient to attract a tax liability EM5156
HMRC already knew about them EM5157
they had telephoned or called at your (or another) HMRC Office and were told there was nothing to do until a return form was received EM5156
the liability depended on technical considerations (for example, a chargeable gain arising on a deemed disposal)
they had been ill, absent or had family or other problems EM5156.