Subject to subsection (2A) below, the rate at which tax is charged under section 65 above on an occasion following one or more ten-year anniversaries after the settlement's commencement shall be the appropriate fraction of the rate at which it was last charged under section 64 (or would have been charged apart from section 66(2)).
Subsection (2A) below applies—
Whether or not all of the property within any of paragraphs (a) to (c) of subsection (2) above has remained relevant property comprised in the settlement, the rate at which tax is charged under section 65 is to be the appropriate fraction of the rate at which it would last have been charged under section 64 above (apart from section 66(2) above) if—
In the case of property within subsection (2)(a) above ... the value to be attributed to it for the purposes of subsection (2A) above is its value immediately after it became comprised in the settlement; and in any other case the value to be so attributed is the value of the property when it became (or last became) relevant property.
For the purposes of this section the appropriate fraction is so many fortieths as there are complete successive quarters in the period beginning with the most recent ten-year anniversary and ending with the day before the occasion of the charge; but subsection (3) of section 68 above shall have effect for the purposes of this subsection as it has effect for the purposes of subsection (2) of that section.