The members of the Customers Council shall be not fewer than eight, nor more than twelve, persons appointed under this paragraph by the Secretary of State from persons who appear to him to have knowledge or experience relevant to the discharge of the functions of the Council but who are not members or employees of any of the new water and sewerage authorities; so however that he shall seek to ensure that the appointees include persons appropriate to represent, both as respects domestic and as respects non-domestic services, the interests of, respectively—