For the sake of of a quiet life, it might be worth allowing him to pay a third just this once, while you two cover the £30 extra you want him to pay, before you can all sit down and agree how you're each going to pay. For the sake of £30, the Nigerian's being ridiculous, yet equally... for the sake of £30, split between you and your other housemate, you could have this sorted amicably without any extra late fees being slapped on. There's no way the Nigerian can moan, he's paying an equal share, and I'm sure for buying peace for £15 each seems like a dream buy, if he's being as anti-social and unreasonable as you suggest.