Speaking to the girlfriend, it turns out that the landlord is demanding back payment for the past 3 months, to the tune of £150!! Totally unreasonable imo, I'm gonna make a counter offer of £20 to cover any water and electricity I might have used. If she rejects that I'm basically gonna have to tell her to screw herself...
I'm not sure if this whole thing is a dig at me or not, because there's other people that often stay round and she's saying she'll charge them too. I think this whole ordeal will just serve to alienate people and lose a tenant, as my girlfriend is now talking about moving out. Things were pretty tense anyway, due to the landlord being pretty unreasonable about other things (e.g. charging for general wear and tear which isn't the tenants responsability). Goes to show it's probably not a good idea to live with your landlord.