Rent a room relief
If you rent out a room in your home, then the good news is that HMRC give you up to £7,500 income tax relief, under the appropriately named Rent a Room Scheme. Note that it's halved to £3,750 if someone else gets income from the property.
This includes if you're renting to a long-term lodger, via platforms such as Airbnb, or even if you're running a guest house.
To qualify you must be offering furnished accommodation in your main home. You don't need to own the property to qualify, but you'll normally need your landlord's permission to sub-let.
See HMRC's guidance for more information.
In untied, you can indicate that you're renting out a room in your home by navigating to Profile > Income > Property. There’s an example from our mobile app below: