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Thanks to everyone for their insights. There are various things he has to consider before definitely deciding to leave. One of those being transport from home to uni!!
He really asked me about this, more to see if I thought he was being unreasonable, as his housemates seem to think he is. I disagree. This girl if freeloading, and they are allowing it. Aside of being in contravention of their rental agreement of course.
I have suggested he might try to go to the university for some advice/help, although apparently the rental house is not connected in any way to the uni. I do agree that he really should also talk to the energy company, I don't know if they allow more than one person to be on the agreement, but frankly it's alarming if one person is being expected to take all the responsibility for it.
The way that these university rental houses are run makes it impossible to each have their own meter, which would be the ideal solution. There is only one bathroom, and a central heating system for the whole house, plus the shared places, sitting room, kitchen. This would make it difficult to have individual meters. Frankly the way they are run (and charged for), is a total racket, and there should be far more oversight. But it is what it is, and for now, he needs to be sure he's going to leave. If he takes this situation to anyone official, they all risk being thrown out. Actually, he does have leverage there, as he could, with a car, commute. The others live too far away to do that.
Hopefully they can sort it out more or less amicably, they were friends during the first year whilst in halls of residence, and it would be a shame to allow this to change that.