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

(a) by substituting the following for subsection (1):

"(1)

(a) For the purposes of this section, references to 'charges on income paid for the purposes of the sale of goods', where they are in the course of a trade in an accounting period, shall be taken to be such amount as would be the amount of the income from the sale of goods in that period if, notwithstanding subsection (4), the reference to 'the company's income for the relevant accounting period from the sale in the course of the trade mentioned in that subsection of goods and merchandise' for the purposes of subsection (3), were to the amount of so much of the charges on income paid wholly and exclusively for the purposes of the trade in that period as appears to the inspector or on appeal to the Appeal Commissioners to be referable to charges on income paid for the purpose of the sale of goods and merchandise.