Just to provide some extra details:
-I live in the UK (England).
-I am renting the whole apartment, not just a room. The Host is not living with me.
From what I have read on the Internet, I don't think the landlord can kick me out without evicting the tenant (Host) first. Seeing as the Host is currently out of the country, I think I'll be fine for the next week or two. As has been said, I believe the landlord needs to issue a notice to the tenant first in order to get him evicted. From what I understand, I have entered into a seperate agreement with the Host. The Host, being the tenant, has some legal rights when residing the property for whatever length of time his tenancy agreement states, i.e. he can't be asked to leave *immediately* without receiving a notice of some duration. Hopefully, this prevents me from being kicked out immediately too.
Fortunately, the landlord seems reasonable enough to let us stay for the duration of the agreement with the Host. I imagine the tenant is probably going to get evicted, or at best will be fined some compensatory amount for breaking his tenancy agreement with the landlord.