Milan is the place to be these days if you’re rich and can stand the pizza. Goldman Sachs Group’s Richard Gnodde, who leads the firm’s businesses outside North America, is among financial executives relocating from London after the U.K. changed its tax rules for foreign residents. Ann Kaplan Mulholland, a Canadian reality-TV star who owns a castle in Kent with her husband, is also making the move, though she bemoans the lack of culinary options in Italy for noncarbohydrate-eating immigrants.

If the campaign against abolition of the "nondom” (nondomiciled) regime is measured by the volume of noise on each side, then the verdict is already in: Britain has made a giant mistake and will rue driving away ultrawealthy individuals who pay (on average) large amounts of tax, enrich the economy with their entrepreneurial talents and fund philanthropic works. A drumbeat of reports of notable departures has grown louder after the nondom privileges ended in early April, along with predictions of the resulting fiscal damage.

The latest contribution comes from the London-based Centre for Economics and Business Research, which recently published a study commissioned by a campaign group calling itself Land of Opportunity. The report says the tax changes could cost the Treasury £7.1 billion ($9.5 billion) if 40% of nondoms — about 80,000 taxpayers — leave. Research by Oxford Economics for another recently formed lobby group named Foreign Investors for Britain estimated a cost of almost £1 billion if 32% depart. A Treasury spokesperson said it didn’t recognize the figures in the CEBR report, noting that the independent Office for Budget Responsibility had "confirmed” the changes would raise £33.8 billion over the next five years. Someone is going to have egg on their face.