NIM29017 | Special cases: Class 1 - mariners: working on a foreign ship - radio officer
From HM Revenue & Customs · National Insurance Manual
Regulation 115 of the Social Security (Contributions) Regulations 2001 (SSCR 2001) (SI 2001 No 1004)
If a mariner is a Radio Officer and works outside the UK, they and their employer, or the person paying their wages, must pay Class 1 NICs if they are domiciled or resident in the UK and their contract of employment was entered into:
in the UK and was intended to be carried out either wholly or partly during the ship’s voyage and
their employer, or the person paying their wages, has a place of business in the UK.
See NIM29003 if the person is resident, or the employer’s business is in the EEA.