4. For the purpose of regulation 3, the Comptroller shall determine —
(a)
the income chargeable to tax of an approved trustee company having regard to such expenses, capital allowances and donations allowable under the Act as are, in his opinion, to be deducted in ascertaining such income; and
(b)
the manner and extent to which any losses arising from the trustee or custodian services specified in that regulation may be deducted under the Act in ascertaining the chargeable income of an approved trustee company.