Hi,
If the total of foreign dividends and UK dividends, exceed the dividend allowance for the tax year, they are required to be reported in a self assessment tax return.
If the foreign dividend exceeds £2000.00, then the dividend should be reported in SA106, including any tax deducted.
You may be able to claim a foreign tax credit relief, for an element of the tax deducted in the other country.
You will need to look at the double taxation agreement in force, to help calculate the relief due in the guidance here
Tax treaties
Thank you.