As six banks get out their chequebooks to pay $4.3 billion in fines for rigging foreign exchange markets, one key question is: what’s the best way of regulating this huge market?

The $5.3 trillion a day market is at present subject only to self-regulation and codes of conduct (although banks and other players in the market have their own regulators). But despite the wrongdoing uncovered in this latest probe, hefty new codes of conduct may not be the result.