(1)Where—
(a)a person works full-time in one or more of the following, that is to say, a trade, profession, vocation, office or employment; and
(b)no part of the trade, profession or vocation is carried on in the United Kingdom and all the duties of the office or employment are performed outside the United Kingdom;
the question whether he is resident in the United Kingdom shall be decided without regard to any place of abode maintained in the United Kingdom for his use.
(2)Where an office or employment is in substance one of which the duties fall in the year of assessment to be performed outside the United Kingdom there shall be treated for the purposes of this section as so performed any duties performed in the United Kingdom the performance of which is merely incidental to the performance of the other duties outside the United Kingdom.