Professor Laffer again.

There is an article this week in the Wall Street Journal by Arthur Laffer and Stephen Moore, giving fresh evidence on the thesis that if you raise tax on the rich you will probably end up with less revenue. (We have seen our own Institute of Fiscal Studies suggest, after careful consideration and examination, that the Chancellor's talk of raising the top rate of income tax to 50% could well end up raising less revenue than before.)

They produce overwhelming evidence that differential upper tax rates cause highly paid and creative people to move to states with lower taxes, and that at the same time the low tax recipient states enjoyed the highest rates of growth. It seems that 1,100 people every day, times 365, moved from high to low tax states between 1998 and 2007.

"Ah,but," say the lefties writing in the Guardian, " where tax rates are lower, services suffer." This has been an article of faith in left circles, chorused whenever their pet doctrines were threatened.

This dictum is shown to be false by Laffer and Moore. New Hampshire is the example of a state with no income or sales taxes but achieves among the best test scores nationally on the provision of social services, even if it spends less. New Jersey 50 years ago with low state taxes attracted creative people. In time it increased taxes, drove people out, and now with high taxes which have mostly benefited public sector jobs, it has among the worst educational services and people are leaving in droves.

The moral seems to be "Don't be an apologist for old time socialists bent on spite, Cameron, reduce the 50p rate to send a message and increase revenue from the rich. Encourage tax competition where you can, - over council tax, perhaps between devolved parts of the UK. The evidence should be more powerful than any mantra."