"How consideration consisting of periodical payments to be charged"
"(2) Where the consideration, or any part of the consideration, for a conveyance on sale consists of money payable periodically for a definite period not exceeding twenty years, or in perpetuity, or for any indefinite period not terminable with life, the conveyance is to be charged in respect of that consideration with ad valorem duty on the total amount which will or may, according to the terms of sale, be payable during the period of twenty years next after the day of the date of the instrument."
"Directions as to duty in certain cases"
"(4). Where a person having contracted for the purchase of any property, but not having obtained a conveyance thereof, contracts to sell the same to any other person, and the property is in consequence conveyed immediately to the sub-purchaser then, except where- (a). the chargeable consideration moving from the sub-purchaser is less than the value of the property immediately before the contract of sale to him, and (b). the conveyance is not one to whichsection 107 of the Finance Act 1981 (sales of houses at discount by local authorities etc) applies, the conveyance is to be charged with ad valorem duty in respect only of the consideration moving from the sub-purchaser. … 1. Any reference in subsection (4) or subsection (5) of this section to chargeable consideration is a reference to consideration which falls to be brought into account in determining the duty (if any) chargeable on the conveyance to the sub-purchaser or, as the case may be, on the conveyance of each of the parts or parcels in question; and in any case where it is necessary for the purposes of either of those subsections to determine the value at any time of any property, that value shall be taken to be the price which the property might reasonably be expected to fetch on a sale at that time in the open market."