§ 18. "That there may be included in any Act of the present Session relating to finance such amendments of Section twenty-one of the Finance Act, 1922 (which relates to Surtax on the undistributed income of certain companies) and of any enactments relating to or amending that Section or referring to apportionments there under, as Parliament may determine, and any such Act may provide that any of the said amendments shall have effect for the purpose of assessments for any year not earlier than the year 1936–37 and authorise any necessary additional assessments for any such year."