SIOG7280 | Information and inspection powers: Schedule 36 FA 2008: non-compliance with a third party notice
From HM Revenue & Customs · Specialist Investigations Operational Guidance
Where a third party notice has not been complied with and proceedings should be taken, a report should be made to the Technical Manager (Powers and Penalties). It will not normally be necessary to send the whole file, but you should send copies of the following documents:
the brief for the approval hearing
your note of what happened at the approval hearing
the opportunity letter
the formal notice
any correspondence exchanged about either the opportunity letter or the notice
a brief note of any other relevant matters, including confirmation that the documents are still necessary to your enquiry.