As a landlord i take it as my responsibility to find out if tenants are staying on at the end of their agreement, and to find alternative tenants so there is no empty period in the house.
That's what the notice period is for, so the landlord can find new tenants. It is a very standard contract that rolls over till you hand notice in. They however sometimes ask you to sign a new contract if they want you of the roll over and back in a minimum term contract.