In this Act ‘default sum’ means, in relation to the debtor or hirer under a regulated agreement, a sum (other than a sum of interest) which is payable by him under the agreement in connection with a breach of the agreement by him.

But a sum is not a default sum in relation to the debtor or hirer simply because, as a consequence of his breach of the agreement, he is required to pay it earlier than he would otherwise have had to.