s 25 Interests in expectancy
25.—(1) When an estate includes an interest in expectancy, estate duty in respect of that interest shall be paid, at the option of the person accountable for the duty, either with the duty in respect of the rest of the estate or when the interest falls into possession. (2) If the duty is not paid with the estate duty in respect of the rest of the estate, then —(a) for the purpose of determining the rate of estate duty in respect of the rest of the estate, the value of the interest shall be its value at the date of the death of the deceased; and (b) the rate of estate duty in respect of the interest when it falls into possession shall be calculated according to its value when it falls into possession, together with the value of the rest of the estate as previously ascertained.