(1) Subject to this section, the high income threshold is the amount prescribed by, or worked out in the manner prescribed by, the regulations.
(2) A regulation made for the purposes of subsection (1) has no effect to the extent that it would have the effect of reducing the amount of the high income threshold.
(a) in prescribing a manner in which the high income threshold is worked out, regulations made for the purposes of subsection (1) specify a particular matter or state of affairs; and
(b) as a result of a change in the matter or state of affairs, the amount of the high income threshold worked out in that manner would, but for this subsection, be less than it was on the last occasion on which this subsection did not apply;
the high income threshold is the amount that it would be if the change had not occurred.