The insurer shall be deemed to have derived in any year, in respect of the premiums paid or payable in that year under such contracts, a taxable income equal to 10% of the total amount of such premiums:
Provided that, where the actual profit or loss derived or made by the insurer
in respect of such premiums is established to the satisfaction of the
Commissioner, the taxable income of the insurer in respect thereof, or the
amount of the loss so made by the insurer shall, subject to this Act, be
calculated by reference to receipts and expenditure taken into account in
calculating that profit or loss.