Also worth noting that by law your room should have a lock on it and if they want to go in there they need to give you 24 hours notice. (unless its on fire or something)
As a live in landlord I'm interested to see this law as it's something I've never heard before!
That's a good point about access to your room though, especially if you've signed a Assured Shorthold Tenancy which I think is the wrong thing.
Basically, if you're a "lodger" you get less rights.
https://www.citizensadvice.org.uk/housing/renting-a-home/subletting-and-lodging/lodging/lodging/
A lodger is someone who lives with you as part of your household sharing some of your accommodation, such as the bathroom or kitchen. They may have their 'own' room, but they live in your home with your permission and don't have the right to exclude you from their room or any part of your home.
http://www.spareroom.co.uk/content/info-flatsharing/rights-for-renters-for-tenants-and-lodgers
Because the flat or house is the landlord's main place of residence, the balance of rights is in their favour. Any contract you sign with this kind of landlord will not be an AST (Assured Shorthold Tenancy - normally with a 6 month break clause and 2 months notice required for a landlord to evict a tenant) but a licence.
If you've signed an Assured Shorthold Tenancy I get the impression they don't know what they're really doing.
Whereas a tenant 'owns' the space they rent during the period of their lease, if you become a lodger, you don't have the right to exclude your landlord from the room you're renting. So, as a lodger, you won't be able to put a lock on the door to your room to keep them out, although they must respect your privacy at all times. What does this mean in practice? They have the right to come into your room, but should always ask in advance, and give you the chance to say no.
By no means is this a law in relation to a lodger though.