Whilst there are different types of tenancy agreements, the most common type is an AST (Assured Shorthold Tenancy). You will generally have an AST if:
Tenancy agreements are not determined by the landlord or agent, but by how the property is occupied. If you are unsure about what type of tenancy agreement you have or should use, refer to Tenancy agreements – GOV.UK for specialist advice. The Government have also produced a model AST along with guidance which can be used by private landlords.