Readers’ forum: Best tax result for room rental

My niece lets out part of her flat and enjoys rent-a-room relief. The rent is more and the bills are less than £7 500 a year so the relief operates by deducting £7 500 from the gross receipts and paying tax only on the excess.

Any contribution above the rent that the lodger makes towards bills is just treated as additional rent – an example at PIM4030 shows this. But what if the lodger pays rent to her and they share the bills 50:50? If she could still deduct £7 500 from the rent and ignore the bills that would appear to give a better result. I cannot find anything in the rules or guidance that explicitly deals with this. If it does ‘work’ would it be necessary to set up a separate bank account to deal with bills to avoid my niece...