And nor, when it comes down to it, will almost any one those who are well off enough to earn more than £80,000 a year flee the country, or even work less, as a result. First, most of those people are on contracts that do not vary pay with tax rates. Second, most people have no clue how much tax they pay. And third, most people work harder when they earn less if (as is true of many of those on high pay) they have fixed and very expensive commitments. The plan does, then, make sense. Inelastic behaviour will result in the higher taxes being settled with little issue arising.
The claim there is that the income effect is greater than the substitution at those high income levels. Which is an empirical claim, as such one that can be tested.
Ah, yes, we did, didn’t we? Ritchie’s wrong.