UK residents with foreign income or gains: capital gains tax: Amount of foreign tax credit relief - extent to which a gain is doubly taxed
As mentioned in INTM169100, credit for foreign tax cannot exceed the UK tax due on the doubly taxed gain. There may be situations where the amount of the UK gain is different from the amount of the gain that is taxed in the other country; or where the period of ownership of the asset that is taken into account in computing the UK gain is different from the period of ownership of the asset that is taken into account in computing the gain in the other country. In either case, the amount of the foreign tax allowable for foreign tax credit relief may need to be restricted. For further details on this, see CG14395 - CG14425.