If,-
(a) the promoter fails to give possession in accordance with the terms of his agreement of a flat duly completed by the date specified, or any further date or dates agreed to by the parties; or
(b) the promoter for reasons beyond his control and of his agents, is unable to give possession of the flat by the date specified, or the further agreed date and a period of three months thereafter, or a further period of three months if those reasons still exist, then, in any such case, the promoter shall be liable on demand (but without prejudice to any other remedies to which he may be liable) to refund the amounts already received by him in respect of the flat (with simple interest at nine per cent per annum from the date he received the sums till the date the amounts and interest thereon is refunded), and the amounts and the interest shall be a charge on the land and the construction, if any, thereon in which the flat is or was to be constructed to the extent of the amount due, but subject to any prior encumbrances.