(1) Section 448 of the Principal Act is amended -

(a) by substituting the following for paragraph (b) of subsection (3):

 "(b) then deducting from the relevant sum any amounts allowed under sections 243A, 396A or 420A against the company's income for the relevant accounting period from the sale of those goods.",

and

(b) by substituting the following for subsection (5A):

"(5A) Where any part of the profits of an accounting period of a company is charged to corporation tax in accordance with section 21A, then for the purposes of this section, the relevant corporation tax shall be reduced by an amount determined by the formula -

where -

R is the rate per cent specified in section 21A(3) in relation to the accounting period, and

S is an amount equal to so much of the profits of the company for the accounting period as are charged to tax in accordance with section 21A.

(5B) Notwithstanding section 4(4)(b), the income of a company, referred to in the expression 'total income brought into charge to corporation tax', for the accounting period for the purposes of subsection (2) shall be the sum determined by section 4(4)(b) for that period reduced -