These agreements are assured shorthold tenancies (ASTs). Most residential properties in England and Wales are let on an AST. An AST allows a landlord to let the property but also allows them to get the property back (repossession). In order to get repossession of the property you must follow the correct procedure or you could be guilty of evicting your tenant illegally.
Tenant eviction is a necessary part of being a landlord. Most of the time repossessing property is fairly straightforward and should happen when a tenancy comes to an end using a Section 21(Form 6A), if the property is located in England.