(1)For the purposes of section 378(1)(b) (deduction from seafarers' earnings: eligibility), duties of an employment as a seafarer which are performed outside the United Kingdom are treated as performed in the United Kingdom if conditions A and B are met.
(2)Condition A is that in the tax year in which the duties are performed the employment is in substance one whose duties fall to be performed in the United Kingdom.
(3)Condition B is that the performance of the duties performed outside the United Kingdom is merely incidental to the performance of duties in the United Kingdom.
(4)Section 39 (duties in UK merely incidental to duties outside UK) does not affect the question—
(a)where any duties are performed, or
(b)whether a person is absent from the United Kingdom,
for the purposes of section 378(1) to (3).