Where a jointly owned property is let, determining for tax purposes how much of the income, profits or losses each owner is responsible for is not always straightforward. It depends on the type of joint ownership, plus there are special rules where the joint owners are married or in a civil partnership.
The Flow Chart - Taxation of Income from Jointly Owned Property will help you work out how much income etc. for tax purposes each owner is responsible for.
Definitions for the flow chart:
Form 17 can be downloaded at https://tinyurl.com/hy4zj64
or completed online at https://tinyurl.com/jhnwesz
Where you own a property as joint tenants you can change to tenants in common by severing the joint tenancy. Where the other joint owner is your spouse/civil partner, Form 17 will allow you vary the share of the property you own and be taxed on your respective shares of income etc.
An Agreement to Sever Joint Tenancy and Deed of Trust for Property can be used in conjuction with the flow chart.