TSEM9868 | Property held jointly by married couples or civil partners: Form 17 rule - married couple or civil partners continue to live together
From HM Revenue & Customs · Trusts, Settlements and Estates Manual
Where a married couple or civil partners continue to live together but their beneficial interests change there are three possibilities
the property is still held in joint names and no declaration is made: the standard 50/50 rule continues to apply after the date of the change
the property is still held in joint names and a fresh declaration is made: the income is split in the way set out in the new declaration; the new split applies from the date of the new declaration
the property is no longer held in joint names: from the date of the changes normal principles apply; if, say, one spouse or civil partner has become the absolute owner of the income and capital then all the income is assessed on him or her.