It is the duty of local authorities to carry this Act into execution in their areas, subject to—
subsection (3) of this section and regulations under section 91ZD,
the provisions of this Act relating to certain other authorities or persons,
the provisions of Part I of the Public Health Act 1936 relating to united districts and joint boards,
section 151 of the Local Government, Planning and Land Act 1980 (urban development areas), and
section 1(3) of the Public Health (Control of Disease) Act 1984 (port health authorities).
It is the function of local authorities to enforce building regulations in their areas, subject to sections 5(3), 48(1) and 53(2) above . . . . —
subsection (3) of this section,
sections 5(3), 48(1) and 53(2), and
regulations under section 91ZD.
In cases where section 91ZA or 91ZB provides that the regulator is the building control authority, it is the duty of the regulator (and not the local authority in question)—
to carry Part 1 of this Act into execution, and
to enforce building regulations.