UK residents with foreign income or gains: claims for double taxation relief against UK tax: method of allowing relief
Allow credit as far as possible against tax chargeable in an assessment on the claimant in respect of the income or gain concerned, or against tax chargeable in any assessment on the claimant’s income if the income or gain concerned is taxed by deduction. If this cannot be done, give credit by discharge or repayment of United Kingdom tax as may be appropriate (but not by repayment of the foreign tax; see INTM161150).
If a paying agent has allowed provisional credit for foreign tax (INTM161010), it is only the actual United Kingdom tax deducted which can be repaid. See the instructions at INTM164520 onwards concerning the adjustment of provisional credit in such cases.