(1)A deduction is allowed from earnings from an employment as a seafarer if—
(a)the earnings 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.
(2)In this Chapter “eligible period” means a period consisting of at least 365 days which is either—
(a)a period of consecutive days of absence from the United Kingdom, or
(b)a combined period.
(3)A combined period is a period—
(a)at least half of the days in which are days of absence from the United Kingdom, and
(b)which consists of 3 consecutive periods, A, B and C, where—
A is a period of consecutive days of absence from the United Kingdom or a period which is itself a combined period,
B is a period of not more than 183 days, and
C is a period of consecutive days of absence from the United Kingdom.
(4)For this purpose a person is only regarded as being absent from the United Kingdom on any day if absent at the end of the day.