Hi,
I direct you to guidance available at
PIM1030 - Introduction: jointly owned property & partnerships which advises-
However, where the joint owners are husband and wife, or civil partners, profits and losses are treated as arising to them in equal shares unless:
both entitlement to the income and the property are in unequal shares, and both spouses, or civil partners, must inform HMRC that their share of profits
and losses is to match the share each holds in the property.
To inform HMRC of unequal shares in a property you must complete a Form 17, enclosing appropriate evidence which shows your unequal shares such as a declaration or deed of assignment, this can be found at
Declare beneficial interests in joint property and income
Thank you.