Original: If the tenancy was entered into after 28th February 1997, and either: the landlord serves a notice on the tenant, saying the tenancy is not an Assured Shorthold Tenancy; or the tenancy agreement says that the tenancy is not an Assured Shorthold.
Simplified: If the tenancy was occupied after 28th February 1997, and either: the landlord gives notice to the tenant. He should say that the tenancy is not an Assured Shorthold Tenancy; or the tenancy agreement says that the tenancy is not an Assured Shorthold.