Can't really answer your question but you should be aware that under the rent a room scheme the most he can receive is 7620 pa, 635 pm in total. Otherwise the total amount is liable to tax subject to normal investment deductions.
Also, are you claiming rent relief? If not tell him that you intend to and ask him for his PPS number See [broken link removed]. Just to let you know that you don't need his PPS number if he refuses.
Get him to amend the agreement to you are each liable to 1/3 of bill etc.
Who's name is going on the bills?
Does he intend living in the house as his PPR?