4S—Where an offer to purchase is served on the person so entitled and he wishes to sell but he considers that a term or condition contained in the offer to purchase is unreasonable, he may request the authority to strike out or vary the term or condition by serving on the authority, within one month after service of the offer to purchase, a notice in writing setting out his request; and if the authority agree they shall accordingly serve an amended offer to purchase within one month of service of the said notice setting out the request.