Where the dwelling-house is reasonably required by the landlord for occupation as a residence for—
(a) himself, or
(b) any son or daughter of his over 18 years of age, or
(c) his father or mother, or
(d) if the dwelling-house is let on or subject to a regulated tenancy, the father or mother of his wife or husband,
and the landlord did not become landlord by purchasing the dwelling-house or any interest therein after 23rd March 1965 or, in the case of a dwelling-house subject to a regulated furnished tenancy, after 24th May 1974 or, if the dwelling-house was on 7th November 1956 let on or subject to a controlled tenancy, after 7th November 1956.