[EM3831A] Concluding the Enquiry: SA Legislation: Elements of partial and final self-assessment Closure Notices – Closure Notice terminology
The guidance on the page explains what is meant by the terminology used in relation to self-assessment closure notices.
ITSA, NRCGT and CTSA enquiries are into returns or claims. Partial closure notices (PCN) and final closure notices (FCN) are only issued for enquiries into returns. Enquiries into claims use different legislation.
HMRC can only enquire into each return once (although we can enquire into an amendment to a return that is made after our enquiry into the return has been completed). So our enquiry is always into the whole return.