2. Any building bye-law in force immediately before 1st October 1973 shall only have effect in relation to—N.I.
(a) plans which, in accordance with building 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.