Use form R43M to claim a tax refund if you're a merchant seafarer not resident in the UK or any other European Economic Area (EEA) State.
If you are a seafarer who is not a resident in the UK or any other EEA country, you may be able to claim back any UK Income Tax taken off your seafaring earnings.
Any income from duties you performed in the UK, or within the UK continental shelf, will be liable to UK tax. So will duties you performed between UK ports where you did not visit a foreign port. Any duties you performed outside that sector or on direct journeys between UK and foreign ports will not be liable to UK tax.