sorry, 搞錯了, 美國會扣15% withholding tax on dividend to UK tax resident
美國扣咗嘅WHT, 英國應該可以用tax credit去抵減UK dividend tax
https://www.irs.gov/pub/irs-trty/uk.pdf
ARTICLE 10 Dividends
(1) Dividends derived from a corporation which is a resident of a Contracting State by a resident of the other Contracting State may be taxed in the other Contracting State. However, such dividends may be taxed in the Contracting State of which the corporation paying the dividends is a resident, but if the beneficial owner is a resident of the other Contracting State, the tax so charged shall not exceed 15 percent of the gross amount of the dividends
UK US double tax relief manual - dividend
https://www.gov.uk/hmrc-internal-manuals/double-taxation-relief/dt19867a
The United States tax deducted from a dividend paid by a United States corporation at the agreement rate of 15 per cent (5 per cent if the recipient is a company which is a resident of the United Kingdom and controls, directly or indirectly, at least 10 per cent of the voting stock in the United States company and doesn’t qualify for zero rate - see below) qualifies for credit as a direct tax