It is ironic that a one-party state should embrace an anti-monopoly law. But since last August China has had one, and is not afraid to use it. So how worried should Rio Tinto and BHP Billiton be by comments from a presumably well-connected official that their proposed tie-up has “strong monopolistic flavours?”

If it plays by the rulebook it approved last year, loosely modeled on European laws, China's primary competition regulator should sit this out. What the world's number two and three iron ore miners are proposing is a production joint venture, not a merger. Since 1998, European authorities have left almost all of these alone. Only when a JV operates autonomously in the marketplace can authorities claim jurisdiction under merger control. If the JV sells only to its parents, as BHP/Rio would do, authorities merely review it under general cartel prohibitions – a much lighter regime, where parties can close ahead of clearance.

Mofcom, the primary Chinese regulator, has yet to share its thoughts on commercial agreements like this, dozens of which are struck daily. But now that one has come along that supplies around 75 per cent of China's iron ore imports, it needs to tread carefully. If it decides it isn't a merger, the file passes to two other vast bureaucracies – the State Administration for Industry and Commerce and the National Development Reform Commission. What happens from that point is anyone's guess; both bodies are still consulting on procedures.