(1) Section 25 (as amended by section 38 of the Finance Act, 1990) of the Finance Act, 1989, shall have effect as respects dividends paid on or after the 6th day of April, 1992, as if in subsection (3)(a) for "6th day of April, 1991," there was substituted "6th day of April, 1997":
Provided that, subject to subsection (2), a company shall not be entitled, by virtue of this section, to specify, in accordance with subsection (1) of the said section 25, that a distribution, being an interim dividend or part of it, is to be treated as made for the accounting period in which it is made where -
(a) the circumstances of the company are such that, if the distribution or the part of it, as the case may be, were treated as made for the accounting period in which it is made, the company would be unable, at the time when the interim dividend is paid, to determine without recourse to estimation, how much of the distribution or the part of it, as the case may be, would, in accordance with subse