1. Any regulations in force immediately before 1st October 1973 which were made under section 23(1) of the Clean Air Act (Northern Ireland) 1964 [1964 c.16] and deemed under subsection (2) of that section to be bye-laws made by a sanitary authority under section 41 of the Public Health (Ireland) Act 1878 [1878 c.52] shall continue to have effect in relation to—N.I.
(a)plans which, in accordance with those bye-laws, were deposited with a local authority before 1st October 1973; and
(b)work carried out in accordance with plans deposited before 1st October 1973, with or without departure or deviations from those plans; and
(c)work carried out and completed before 1st October 1973;
and in this paragraph “local authority” means the council of a borough, county borough or of an urban or rural district.