Paragraph 3

by virtue of any provision made by or under any Act, employers of any class are required, in taking persons of any class into their employment (whether in all cases or not and whether absolutely or subject to exceptions), to restrict themselves to, or to give preference to, persons for the time being included in a specified pool or register, and

under that provision, all persons included in that pool or register are in the employment of a specified body when not otherwise employed, and

the occupation in which a person who has entered on a period of whole-time service was last employed before the beginning of that service is such that the taking of him into employment by the person who, but for the provisions of this paragraph, would be his former employer is affected by that provision,