TSEM9952 | Ownership and income tax: Specific types of property: bank and building society accounts: example 11: joint names of married couple - 50/50 rule applies
From HM Revenue & Customs · Trusts, Settlements and Estates Manual
A and B, a married couple living together, open a bank account in their joint names. A claims that the interest should be taxed on B only, as B alone provided the funds for the bank account.