Although it's not strictly necessary to have one to create a valid assured shorthold tenancy in England and Wales, all landlords should ensure that their tenants have signed a written tenancy agreement prior to going into possession. However, do note that in Scotland it's necessary to have a written tenancy agreement for it to be a short assured tenancy.

Informal oral arrangements can be a recipe for disaster:

• If a tenancy is oral, there may be arguments later about its terms, even if these were clearly discussed when the tenant went in.
  
  
• You will not be able to use the accelerated possession procedure to evict the tenant, where there is no written tenancy agreement.
  
  
• Once a tenant is in occupation, you cannot then force him to sign an agreement that varies the terms of his tenancy, so it's essential that this is done before they go in.
  
  
• The landlord will need a formal agreement so he/she can insert clauses that will protect his/her position and regulate the tenant's use of the property.
  
  
• If no written tenancy agreement is provided, a landlord is required by law to provide the tenant with written details of the main terms of his tenancy within six months; so he might as well provide a proper written tenancy agreement to begin with.

Although all tenancies should have a formal written tenancy agreement, this is not always essential with licences. For example, it may not always be necessary in the following circumstances:

1. Bed-and-breakfast accommodation
   
   
2. Letting a room in your house to lodgers.

However, even if a formal letting agreement is not provided in these circumstances, there should always be some paperwork to prove the terms of the letting, in case there is a dispute at a later date.

Law as stated as at 1 February 2006