NIM39620 - National Insurance Numbers (NINOs): Special Cases: Isle of Man Cases
You should check the other guidance available on GOV.UK from HMRC as Brexit updates to those pages are being prioritised before manuals.
The Isle of Man (IOM) and HMRC have historically operated similar National Insurance contribution (NIC) and Social Security schemes. This has allowed us to operate one National Insurance account for a customer who has lived / worked in both territories. The territory in which the customer resides normally holds and maintains the account.
New State Pension (nSP) came into force for customers with a State Pension age (SPa) of 06/04/16 or later. The IOM did not adopt the nSP changes. The IOM will continue to administer the current State Pension scheme including Additional Pension and Guaranteed Minimum Pension together with the retirement allowance only paid there.