If you have a spare room, you can take advantage of the Government's 'Rent a Room' scheme which lets you earn tax-free income up to a certain threshold from letting out furnished accommodation in your home. You can find out the threshold you can earn that will be tax-free on the Government's website. Taking on a lodger can prove a tax-efficient method of supplementing your income but it's important to get the details right. A written Lodger agreement (or Lodger agreement for Scotland) sets out matters such as rent, deposit and the rights and responsibilities of both lodger and landlord. It also enables you to ask your lodger to leave if you need to get your room back. For more information, read Taking in a lodger.
Sharing property ownership or renting out parts of your property to others can be a useful way of splitting costs or supplementing your income, but ensure that you protect your interests by formalising things with relevant documents.