Here's the relevant bit I'm talking about, specifically point 2:
f you have an assured shorthold tenancy, you're usually committed to renting the property for six months or a year.
Before this time is up, you need to decide what to do next. You could:
1. sign a new fixed-term tenancy agreement
2. do nothing and automatically move to a month-to-month tenancy – also known as a periodic or rolling tenancy
3. tell your landlord that you're going to move out at the end of your contract
Read the UK government's guide How to rent for more information on renting a home.