(1)If—
(a)section 378 (deduction from seafarers' earnings: eligibility) applies to earnings for a tax year, and
(b)in the tax year the employee performs some of the duties of the employment as a seafarer or of any associated employments in the United Kingdom,
the amount of earnings in respect of which the deduction under this Chapter is allowed is subject to the following limitation.
(2)The amount is restricted to the proportion of the aggregate earnings for that year from the employment as a seafarer and all associated employments that is reasonable having regard to—
(a)the nature of and time devoted to the duties performed outside and in the United Kingdom, and
(b)all other relevant circumstances.
(3)In this section “associated employments” means employments with the same employer or with associated employers.
(4)The same rules for determining whether employers are associated apply for the purposes of this section as apply for section 24(4) (limit on chargeable overseas earnings where duties of associated employment performed in UK) (see section 24(5)).