What is a tenancy agreement?

The written record of what you and the tenant have agreed. It is not what creates the tenancy, and it cannot override the law.

Since 1 May 2026 every assured tenancy in England is periodic by law, so the agreement no longer sets a fixed term. What it usefully does is record the rent, the payment date, the deposit, who is responsible for what, and any permissions such as pets.

Anything in an agreement that contradicts the statutory position is unenforceable. You cannot contract out of the possession grounds, the rent increase process or the deposit rules by writing something different.