(1) Section 16 of the Principal Act is hereby amended -

(a) by the substitution of the following subsection for subsection (1):

"(1)

(a) The market value of each share in a private company which (after the taking of the gift or of the inheritance) is, on the date of the gift or on the date of the inheritance, a company controlled by the donee or successor, shall be ascertained by the Commissioners, for the purposes of tax, as if, on the date on which the market value is to be ascertained, it formed an apportioned part of the market value of a group of shares in that company, such apportionment, as between shares of a particular class, to be by reference to nominal amount, and, as between different classes of shares, to have due regard to the rights attaching to each of the different classes.

(b) For the purpose of ascertaining the market value of a share in a private company in the manner described in paragraph (a), the benefit to any private company (in this paragraph referred to as 'the first-mentioned company') by virtue of its ownership of an interest in shares in another private company (in this paragraph referred to as 'the second-mentioned company'), shall, where each of the companies so connected is a company which (after the taking of the gift or of the inheritance) is, on the date of the gift or on the date of the inheritance, a company controlled by the donee or successor, be deemed to be -