This paragraph applies where, on a disposal of a house under section 8, in accordance with a consent given by the Housing Corporation under section 9, a discount has been given to the purchaser by the housing association; but this paragraph does not apply in any such case if the consent so provides.

On the disposal the conveyance, grant or assignment shall contain a covenant binding on the purchaser and his successors in title to pay to the housing association on demand, if within a period of F1three years there is a relevant disposal which is not an exempted disposal (but if there is more than one such disposal then only on the first of them), an amount equal to the discount reduced by F1one-third for each complete year which has elapsed after the conveyance, grant or assignment, and before the further disposal.