Tron - let them go - just keep the money here - money earned in the UK taxed in the UK - so what does it matter if they go. Good riddance I say.
Some wonderful Trotsky thinking there. FWIW I'm well below the 40% band, and given I don't feel that poor, I reckon people earning that much are well enough off to afford it. Don't even have an issue with 50% tax at 100k - though I suspect you may already be into the point where such taxation doesn't raise anywhere near as much as you expect due to the side-effects. Still nowhere near filling the black hole, and any taxation beyond that really does become ideological politics of envy rather than an effective method of revenue generation.
If you want examples, high levels of taxation have been tried before (under Wilson/Callaghan?) - go and check just how much revenue they really made.