When does skilful arbitrage turn into illegal market manipulation? The issue is a subtle one, and it is about to be tested. The US Treasury and the Federal Reserve have met the 22 banks that make a market in US Treasury bonds, the hugely liquid market that sets the baseline for the rest of the global financial system, to look for ways to “strengthen market integrity”.

This follows mounting concern from regulators about practices in the US bond market. So far, the affair appears only to have cost the job of one trader at Credit Suisse, while two other traders at UBS are negotiating their departure. There is no reason, at least so far, to expect this affair to match the 1991 scandal in which Salomon Brothers, then the most powerful bank in the market, was found to be trying to manipulate the regular Treasury auctions.