If you live in the same house as the owner, and this includes a house divided into separate flats, then you have a resident Landlord and will have an excluded tenancy. If your friend's parents own the property and your contract is with the parents then you will have more rights than an excluded tenant - see Assured Shorthold Tenancies below.
Excluded tenants have limited security.
There is no legal requirement to have a written agreement for an excluded tenancy but we strongly advise having something in writing that gives the address, name of the Landlord and tenant, period of the letting, rent, deposit, how the deposit will be repaid, how bills will be charged, period of notice on both sides, any special arrangements for using the shared areas and facilities such as telephone or washing machine. Excluded contracts are often for a fixed term, see more on this below. Assured Shorthold Tenancies . For lettings where the Landlord is not in the property an Assured Shorthold Tenancy will be granted. Once you sign you are bound by the terms of the contract.