2. Where any income of a person is not part of his total income by reason only that—
(a)he is not resident, ordinarily resident or domiciled in the United Kingdom, or
(b)the income does not arise in the United Kingdom, or
(c)the income arises from an office or employment, income from which is exempt from tax in pursuance of any enactment,
his income for the purposes of these Regulations shall be computed as though the income first mentioned in this paragraph were part of his total income.