The appropriate national authority may be building regulations delegate to a person or body, to such extent and subject to such conditions as the appropriate national authority may think fit, the powers of approval conferred ... by section 12 above.
So far as those powers are for the time being so delegated to a person or body, section 12 above, except subsection (7) as far as the end of paragraph (a), and any building regulations made by virtue of subsection (7) shall (subject to any prescribed conditions) have effect in relation to that person or body with the substitution of references to that person or body for references to the appropriate national authority.