Subject to subsection (2) and section 4(1A), a person is for the purposes of this Part the landlord in relation to any premises consisting of the whole or part of a building if he is—
Where the person who is, in accordance with subsection (1), the landlord in relation to any such premises for the purposes of this Part ("the immediate landlord") is himself a tenant of those premises under a tenancy which is either—
the superior landlord shall also be regarded as the landlord in relation to those premises for the purposes of this Part and, if the superior landlord is himself a tenant of those premises under a tenancy falling within paragraph (a) or (b) above, the person who is the landlord under that tenancy shall also be so regarded (and so on).