“A deduction is allowed from earnings from an employment as a seafarer if— (a) the earning are taxable earnings under section 15 or 21 (earnings for year when employee resident and ordinarily resident in UK), (b) the duties of the employment are performed wholly or partly outside the United Kingdom, and (c) any of those duties are performed in the course of an eligible period.”
“(1) For the purposes of the Tax Acts, unless the context otherwise requires, ‘offshore installation’ means a structure which is, is to be, or has been, put to a use specified in subsection (2) while— (a) standing in any waters (b) stationed (by whatever means) in any waters, or (c) standing on the foreshore or other land intermittently covered with water. (2) The uses are— (a) use for the purposes of exploiting mineral resources by means of a well; (b) use for the purposes of exploration with a view to exploiting mineral resources by means of a well; (c) use for the storage of gas in or under the shore or the bed of any waters; (d) use for the recovery of gas so stored; (e) use for the conveyance of things by means of a pipe; (f) use mainly for the provision of accommodation for persons who work on or from a structure which is, is to be, or has been, put to a use specified in any of paragraphs (a) to (e) while— (i) standing in any waters (ii) stationed (by whatever means) in any waters, or (iii) standing on the foreshore or other land intermittently covered with water … (4) In this section ‘structure’ includes a ship or other vessel.”