TSEM9978 | Ownership and income tax: Specific types of property: shares: example 8: joint names of civil partners - 50/50 rule applies
From HM Revenue & Customs · Trusts, Settlements and Estates Manual
A and B, civil partners who live together, hold shares in Z plc in their joint names. A provided all the funds to purchase the shares. A resulting trust to A would otherwise apply (TSEM9600), but the specific tax legislation on ITA/S836 provides that A and B are taxable 50/50 on the income (TSEM9814).
The shares are not in a close company (TSEM9822), so S836 does not exclude them.