6Where a custodian releases to the executor of any person everything in his hands to which the executor would, but for the operation of the law relating to trading with the enemy, be entitled, the executor shall be accountable for all estate duty and interest on estate duty for the satisfaction of which the property released is, or but for the operation of the said law would have been, available, in so far as that duty and interest remains unpaid and the custodian shall cease to be accountable therefor.