Where any part of the hire-purchase price payable under a hire-purchase agreement has been paid to the owner pursuant to a contract of loan made between the hirer and any third party and the hire-purchase agreement contains a covenant by the owner to guarantee the hirer's liability under such contract, then for the purpose of calculating the hirer's liability to the owner on termination of the agreement whether by the owner or by the hirer any sum paid by the owner or for which the owner is liable under such covenant at the date of such termination shall be deemed not to have been paid by the hirer under the hire-purchase agreement.—[Mr. Darling.]