In this Part "relevant interest", in relation to a dwelling, means the freehold or a long tenancy, not being in either case subject to a long tenancy.
A tenancy is a long tenancy for this purpose, subject to subsection (3), if it is—
a tenancy granted for a term certain exceeding 21 years, whether or not it is (or may become) terminable before the end of that term by notice given by or to the tenant or by re-entry, forfeiture or otherwise,
a tenancy granted in pursuance of Part V (the right to buy), or
a tenancy for a term fixed by law under a grant with a covenant or obligation for perpetual renewal, unless it is a tenancy by sub-demise from one which is not a long tenancy.
A tenancy is not a long tenancy for this purpose if it is—
an interest created by way of security and liable to termination by the exercise of a right of redemption or otherwise, or
a secure tenancy.
References in this part to an interest in a dwelling are to an interest in land which is or includes the dwelling.