Seafarer's Earnings Deduction explained

You can qualify for the Seafarer's Earnings Deduction as a seafarer if:

You perform all your duties on a ship, or
You perform most of your duties on a ship, and the other duties are incidental to the duties on the ship.

The word 'ship' is not defined in tax law, but 'offshore installations' used in the offshore oil and gas industry are specifically identified and are not regarded as 'ships' for the purposes of the Seafarer's Earnings Deduction. The following list of 'offshore installations' is given as a guide only:

Fixed production platforms
Floating production platforms
Floating storage units
Floating production storage and offloading vessels (FPSOs)
Mobile offshore drilling units (drillships, semi-submersible and jack-ups)
Flotels.

If you work on an offshore installation anywhere in the world, you are not regarded as a 'seafarer' for the purposes of the Seafarer's Earnings Deduction and so cannot claim the Deduction. The employment duties of a seafarer are regarded as being performed outside the UK if they are carried out on a vessel that is engaged on a voyage or part voyage which begins or ends outside the UK. For this purpose, the UK sector of the North Sea is treated as part of the UK. If you had more than one employment in the qualifying period, you may only claim Seafarer's Earnings Deduction for those in which you performed duties outside the UK. A 'qualifying period' is made up mainly of days when you are absent from the UK. You are absent from the UK on a particular day if you are outside the UK at midnight at the end of that day. Non-work days spent outside the UK may be counted as days of absence. A return visit to the UK can also count towards the 'qualifying period' if:

No single return visit lasts for more than 183 consecutive days, and
The total number of intervening days you have spent in the UK is not more than one-half of the total number of days from your first day abroad to the last day of the period you spent abroad after that return visit. Intervening days in the UK may only be counted if they occur between periods of absence. You cannot, for example, make a claim for a period of 365 days which consists of 183 days abroad followed by 182 days in the UK.