I’ve just been looking this up on tinternet and I’ve found some useful information on the ODPM website:
Letting rooms in your home: a guide for resident landlords
You should read this booklet if you are letting (or thinking of letting) part of your only or main home. Published 2003.
Renting rooms in someone’s home
You should read this booklet if you rent (or are thinking of renting)in a property where the landlord also lives. Published May 2002.