Section 19 of the Principal Act is amended -

(a) in subsection (1), by the insertion of "or in relation to which the Commission has made a requirement under section 18A(1) before it is put into effect," after "in accordance with that subsection,",

(b) by the substitution of the following subsection for subsection (2):

"(2) Any such merger or acquisition which purports to be put into effect, where that putting into effect contravenes subsection (1), is void and shall remain void -

(a) until the Commission informs the undertakings which made the notification that the merger or acquisition may be put into effect in accordance with section 21(2)(a), or

(b) where the Commission makes a determination pursuant to section 21(2)(b) to carry out an investigation under section 22 in relation to the merger or acquisition, until a determination is issued under paragraph (a) or (c) of section 22(3).",

(c) in subsection (6)(b), by the substitution of "a notification of a merger or acquisition, a requirement or requirements of one or more of the undertakings involved in such merger or acquisition" for "the notification of the merger or acquisition concerned under section 18, a requirement or requirements of one or more of the undertakings concerned",