How big is too big to rig? Forex trading may soon answer this question, as investigations into possible breaches begin on both sides of the Atlantic. Even a market that trades $5.3 trillion per day may not be beyond the ability of unscrupulous traders. But, is it realistic to expect forex markets ever to be truly fair and transparent?

Central banks around the world routinely intervene to support exchange rate targets. Indeed, the recent currency volatility in emerging markets seems to have led to increased intervention, some of it done in complex ways that minimise use of foreign exchange reserves for currency support. If forex trading is so distorted, how can regulators separate out any wrongdoing from the legitimate actions of central banks? This month, the US Justice Department announced it was looking at forex manipulation, following earlier announcements of a UK Financial Conduct Authority probe and from the Swiss Financial Markets Supervisory Authority. While currencies are hard to move, if information is shared and some client orders are pooled, there could be potential for gain.