Notwithstanding any provision of the Corporation Tax Acts, income arising to the Housing Finance Agency plc -
(a) from the business of making loans and advances under section 5 of the Housing Finance Agency Act, 1981, which income would but for this section have been chargeable to corporation tax under Case I of Schedule D, and
(b) which income would but for this section have been chargeable to corporation tax under Case III of Schedule D,
shall be exempt from corporation tax.