21. Guarantor not to be bound in certain cases

Where a guarantor of the performance of the obligations of the hirer under a hire-purchase agreement enters into an agreement binding the guarantor —

to pay to the owner an aggregate sum which is larger than the balance originally payable under the agreement; or

to perform an obligation in respect of goods other than the goods comprised in the hire-purchase agreement,the agreement so entered shall be void unless the agreement is executed by the guarantor in the presence of a Magistrate.