The United Kingdom does not levy withholding tax on dividends, except for dividend distributions from real estate investment trusts “REITs” which are subject to 20% UK dividend withholding tax.
UK dividend withholding tax recovery
How to get a refund of UK dividend withholding tax?
While the UK does not normally levy dividend withholding tax, qualifying non-residents have the opportunity to claim repayment of some or all of the tax that is deducted from property income dividends that are paid by UK-REITs under a number of double taxation agreements.
Detailed information on UK dividend withholding tax on REIT distributions can be found here: https://www.gov.uk/guidance/double-taxation-relief-for-companies#property-income-distributions-paid-by-uk-real-estate-investment-trusts-reits.