Some seven years ago, Kerr Neilson found himself sitting next to Melinda Gates. The billionaire philanthropist and her then husband, Microsoft co-founder Bill Gates, were in town and attending a dinner thrown by the Pratts.

“How about joining the Giving Pledge?” she later asked Mr Neilson in a letter, according to his recollection, referring to a campaign launched by the Gates and Warren Buffett asking the world’s richest people to give the majority of their wealth to philanthropic organisations.