A lease has a "long term" in any of cases A to D.
Case A: the lease is granted for a term certain exceeding 21 years.
Case B: section 149(6) of the Law of Property Act 1925 applies to the lease (lease granted for life or until marriage or civil partnership) and the lease accordingly takes effect with a term fixed by law.
Case C: the lease is granted with a covenant or obligation for perpetual renewal and accordingly takes effect with a term fixed by law - unless it is a sub-lease with a term fixed by law of 21 years or shorter.
Case D: the lease is capable of forming part of a series of leases whose terms would extend beyond 21 years (see section 4).
In determining whether a lease has a long term, it is irrelevant if the lease is, or may become, terminable by notice, re-entry or forfeiture.