Where any authority (by whatever name called), other than a Commission appointed under section 3, has been or is set up under any resolution or order of the appropriate Government for the purpose of making an inquiry into any definite matter of public importance and that Government is of opinion that all or any of the provisions of this Act should be made applicable to that authority, that Government may, subject to the prohibition contained in the proviso to sub section (1) of section 3, by notification in the Official Gazette, direct that the said provisions of this Act shall apply to that authority, and on the issue of such a notification, that authority shall be deemed to be a Commission appointed under section 3 for the purposes of this Act.