Hi.If I were you, I'd structure any verbal or written agreement in such a way as to show that your mother is simply contributing to the cost of the running of the household to ensure that any cash exchanged has no tax implications for you. Many people have elderly parents living with them and arrange things in the way I've just described. It's certainly the way I'd do it.You could if you wished use the rent a room scheme which allows you to let a room in your home and receive up to £4,250 per annum tax free. Anything you receive over and above that would be taxable. Alternatively, you disclose all the rent and claim a proportion of household expenses against it. Take a look here for more information on the rent a room scheme and here for information on the types of expenses you can claim.There is no maximum amount you can charge any tenant. That's simply down to market forces in your area. As I said at the start, in order to avoid having any need to get involved with the tax office, you should come to an agreement with your mother over a level of contribution towards the household expenses.I hope this helps but let me know if you have any further questions.