Article 10(2)(b) of the UK and USA double taxation agreement allows for both countries to tax the dividends and limits Foreign Tax Credit Relief for dividends to a maximum of 15%.
Uk/USA Double Taxation Agreement - 2002
In the section of the online tax return for foreign dividends, you should enter a reference for the dividends (to help you identify them), the country they are from, the amount of dividend and the tax deducted. The special witholding tax box is for tax deducted under the terms of the European Savings Directive and equivalent third party agreements. This tax will be in addition to any foreign tax deducted by the country of origin of the payment. Please select the rate of 15% and then select yes to the Foreign Tax Credit Relief, only if you want to claim this relief. Click 'add'. Repeat this process until you have entered all of the dividends. You should complete all of the tax return before viewing your calculation. Take a note of the tax due on your dividends. The FTCR is up to a maximum of 15% of the tax deducted in the USA.