When Robert Putnam published “Bowling Alone” six years ago, the book brought the Harvard professor such fame he was invited to speak at Camp David, 10 Downing Street - and Buckingham Palace.

When he arrived to meet the Queen, he found Her Majesty absent but her top courtiers anxious to hear his advice for a multi-racial Britain. Noting that great royal houses had often used marriage to forge important political alliances, he advised them to “go look for a nice Bangladeshi girl for one of the royal princes”. There was dead silence. “No-one spoke,” he said. “Later, the man from Downing Street who had taken me there said, ‘Bob, maybe that wasn’t quite what they wanted to hear.’ ”