Where—
(a)arrangements provide, in relation to dividends of some classes but not in relation to dividends of other classes, that underlying tax is to be taken into account in considering whether any, and if so what, credit is to be allowed against the United Kingdom taxes in respect of the dividends; and
(b)a dividend is paid which is not of a class in relation to which the arrangements so provide;
then, if the dividend is paid to a company which controls directly or indirectly, or is a subsidiary of a company which controls directly or indirectly, not less than 10 per cent. of the voting power in the company paying the dividend, credit shall be allowed as if the dividend were a dividend of a class in relation to which the arrangements so provide.