Hi,
Non resident individuals, who have UK interest and, or, dividends, are taxed on the interest and, or, dividends under disregarded income. Your tax liability is calculated and compared against a second calculation of tax liability, that includes disregarded income. The tax liability is then the lower of the two calculations.
If you have paid too much tax, a repayment can be made and if you have not been taxed enough, then the amount of tax already paid is the tax payable.
Disregarded income will be calculated when you complete your tax return for UK interest and, or, dividends and also SA109, to confirm that you are not resident and claim personal allowances.
HS300 covers non residents and investment income:
HS300 Non-residents and investment income (2023)
Thank you.