(a) There shall be treated as a specified distribution for the purposes of subsection (4) so much of a distribution (in this paragraph referred to as "the first-mentioned distribution") treated under subsection (2) or section 154 as made by a company for an accounting period as does not exceed the amount, which may be nil, determined by the formula -
where, subject to sections 148 and 149 and paragraphs 5 and 6 of Schedule 32 -
A is the amount of the company's income, the corporation tax referable to which is reduced under section 448, for the relevant accounting period which coincides with or is included in the accounting period,
B is the amount of the corporation tax, as reduced under section 448, referable to the amount mentioned in the definition of "A",
E is the amount of the relevant distributions, whether made before the 6th day of April, 1989, or on or after that day, received by the company in the accounting period, which is included in its franked investment income