Six weeks after Bill Gates and Warren Buffett launched their campaign to persuade US billionaires to donate at least half of their fortunes to charity, 40 have already agreed to do so. The two have been contacting the US super-rich individually, a tactic which has apparently paid off. The pledgers include the likes of Ted Turner, Michael Bloomberg, Barron Hilton and Star Wars director George Lucas.

Though it might seem churlish to pick holes in such a potentially spectacular outpouring of private generosity for public good – Gates and Buffett estimate their efforts could generate $600 billion dollars in charitable giving – scepticism has focused on two areas. The pledge does not extend to specifying particular causes. Pablo Eisenberg of the Georgetown Public Policy Institute remarks that ultra-wealthy donors tend to give to causes such as higher education, the arts and established healthcare institutions, with relatively little going towards poverty reduction or disadvantage. ‘I’m not sure tax receipts haven’t done a better job, over time, of meeting the needs of our neediest people,’ he is quoted as saying in the UK’s Guardian newspaper.