Under housing law, a tenant who shares accommodation with the landlord is known as an EXCLUDED OCCUPIER.
As previously mentioned on here, the only notice you have to give is "reasonable" notice. So if you think 7 days is reasonable for him, give him 7 days! This can be verbal or written.
If theres no tenancy agreement, you let him stay out of "good will" etc, it should be this simple. If there are any other complications, have a look at this website
http://england.shelter.org.uk/