“Our culture must be one where the interests of customers and clients are at the very heart of every decision we make; where we all act with trust and integrity.” The words are from a recent speech by Bob Diamond, chief executive of British bank Barclays. In a way, this is just the usual corporate guff. No boss will tell the world about untrustworthy workers who try to harm customers. But Diamond’s aspirations are a particular challenge for the financial industry.