There are different types of tenancy agreement and the type used is not determined by the landlord, but by how the property is occupied. Your tenant is likely to have an assured shorthold tenancy if:
you are a private landlord
the tenancy began on or after 28 February 1997
the house or flat is let as separate accommodation and is your tenant’s main home.
If you are not sure what sort of tenancy agreement you should use please refer to Tenancy agreements - GOV.UK and seek specialist advice.
The Government have produced a model tenancy agreement and accompanying guidance for use by private sector landlords where an assured shorthold tenancy is being entered into.