This part of GOV.UK is being rebuilt – find out what beta means

HMRC internal manual

International Manual

Double Taxation applications and claims: Vouchers: Vouchers showing foreign tax

You may receive a voucher for a foreign dividend which shows foreign tax deducted at source and incorrectly included in claims. This tax is not available for repayment by HMRC.

It may not always be immediately obvious that the tax is foreign. So you need to consider the rate at which tax has been deducted in reaching a conclusion.

As always, reference to COTAX and the HMRC Office it identifies, or does not identify for a wholly foreign company, will form your guidance of last resort.