TSEM3675 - Trust income and gains: relief for overseas tax: expenses of discretionary trust
If trustees are claiming relief for overseas tax they will usually regard expenses as paid out of UK income. This means they can certify the overseas income to the beneficiaries under ICTA88/S809 (TSEM3680).
They may sometimes regard expenses as paid from overseas income. This could be because there is not sufficient UK income to cover the expenses. Or maybe certification is not advantageous to the beneficiary.
Trustees cannot certify, under S809, the overseas income they set against the expenses.