(1) This section shall apply where section 845(4) applies to a business for any accounting period.

(2) Up to the amount determined under this section (in this section referred to as "the amount ineligible for relief"), interest becoming due for payment on money borrowed for the purposes of the business -

(a) shall be excluded in any computation under the Tax Acts of the profits or loss arising from the business, and

(b) shall be excluded from the definition of "charges on income" in section 243.

(3) In determining the amount ineligible for relief, account shall be taken of all money borrowed for the purposes of the business outstanding in the accounting period up to the total cost of the tax-free securities held for the purposes of the business in that period; but account shall not be taken of any borrowed money carrying interest which apart from subsection (2) would not be included in the computation under paragraph (a) of that subsection and would not be treated as a charge on income for the purposes of the Corporation Tax Acts.