NIM24700 | Class 4 NICs: administration: assessment and collection
From HM Revenue & Customs · National Insurance Manual
Section 16 of the Social Security Contributions and Benefits Act (SSCBA) 1992
S16 of SSCBA 1992 provides for the application of the Income Tax Acts to Class 4 NICs. This means that Class 4 NICs are assessed and collected in the same way as Income Tax.