In relation to a holding situated partly outside England, the amount of any sum payable by the Secretary of State by way of hill farm allowance or related less favoured area allowance, whether as principal or on behalf of any other competent authority, may, without prejudice to the amount of any sum payable by the Secretary of State to any other competent authority, be set off against the amount of any sum recoverable from the claimant by the Secretary of State, whether as principal or on behalf of such other competent authority.