any tax chargeable on a person which is postponed under subsection (4)(b) of section 17 of the 1979 Act shall continue to be postponed until that person becomes absolutely entitled to the part of the settled property concerned or disposes of the whole or part of his interest, as mentioned in that subsection; and

section 70 of and Schedule 14 to the [1984 c. 43] Finance Act 1984 shall continue to have effect in relation to amounts of tax which are postponed under that Schedule, and accordingly in paragraph 12 of that Schedule the references to section 80 of the [1981 c. 35.] Finance Act 1981 and to subsections (3) and (4) of that section include references to section 87 of this Act and subsections (4) and (5) of that section respectively.