Rent to a friend

1) Even if you don't perceive a 'profit', you would have to pay tax on 'rent income - mortgage interest - repairs / bills / etc costs' Note part of your mortgage payment will pay down capital which is not tax deductible.

2) Landlord obligations still apply, e.g. gas safety check, EPC, protect deposit if you take one, repairs, check friend's right to rent, friend's right to quiet enjoyment

3) Mortgage: you will need to request Consent to Let from your lender. IF you have just started the mortgage and will be letting the property fairly soon, the lender may think that was your plan all along and refuse CTL, or give CTL for a limited period e.g. 12 months. Then you would need to change to a Buy to Let mortgage (with a maximum 75% loan relative to the property value) and likely higher interest rates.

4) I would suggest you get a formal tenancy agreement and inventory at the start, so everyone knows their responsibilities and is on the same page. If there is a misunderstanding or people mis remember, the deposit resolution / courts can ultimately decide but you would likely ruin a friendship.

Be in absolutely no doubt that doing this will make you a landlord - family, friend, it doesn't matter, you are a landlord in the eyes of the law and have to follow the laws for landlords as described above.