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Ross Brawn's position as FOTA's technical director is now untenable, said Flavio Briatore in Shanghai, furious at the FIA's rubber-stamping of the twin diffuser at the appeal court, angered at the £5 million his team will need to spend to reconfigure its car.

He was further irritated that the seats of his private jet had to be removed to transport the new floors for the Renaults, mood made yet bluer when said floors were held up in customs.

But that's by the by. Briatore's reasoning makes some sense; that the twin diffusers surely go against what the 2009 regulations were trying to achieve. But his insistence that Ross should stand down, that he's pulled a fast one, doesn't stack up. To understand why requires a bit of background.

When Brawn arrived at Honda in late 2007, he was intrigued at how tiny Super Aguri had been making a version of the 2006 Honda that was often embarrassingly faster than the official 2007 Honda. As Aguri went into its death throes, Ben Wood's aero group moved back to the parent team and was tasked by Brawn in September 2007 to begin work on the 2009 Honda.

Concurrently, in Honda's R&D department in Tochigi, a bright young aerodynamicist had given some thought to the proposed 2009 aero regs and come up with the twin diffuser idea. This was incorporated into the design Wood and his team were building up.

Within six weeks of starting the study, they were at 80 per cent of 2007 levels of downforce, already way in excess of the FIA's hoped-for 50 per cent. Brawn, in his FOTA technical director capacity, suggested to the other team technical representatives that maybe they should look at tidying up the regs they themselves had proposed.

He wasn't about to tell them what he had in mind, just that he was aware of a few areas that could be exploited, so why not tidy up the regs while there was still a chance. This would require unanimous agreement from the team representatives. Those of BMW and Renault - that's Flavio Briatore's Renault - said no. So it couldn't go through, and Ross could not do anything other than exploit the possibilities he saw. When Brawn reported it was already at 80 per cent of 2007 downforce, the others put that down simply to the 2007 Honda being so bad.

So why did those two teams object to the tightening of the regs before it was too late? Usually in such cases it's because teams believe they've spotted something the others might not have. So maybe, for example, Renault's treatment of the area ahead of the sidepod, where they found room to insert a vertical bargeboard, was something they didn't want to surrender and in so doing they left the door open for Brawn - and Toyota and Williams - to do the twin diffuser. So it's not really on for Flavio to be complaining now.

Renault was also looking at the twin diffuser concept, but saw a slightly different way of achieving the necessary slots than leaving a horizontal gap between the reference plane and the step plane. It was looking at a more intricate way than just considering the step and reference planes as separate surfaces (the crucial thing that makes the slots legal). They were looking to create a hidden slot by playing with the tolerances of the step and reference plane and having an inverted angle between them.

They asked FIA technical delegate Charlie Whiting for permission for this specific thing and were refused. Hence Renault's claim that they weren't allowed to do what Brawn, Toyota and Williams were. The reality is they were asking for something that would have had a similar effect but the legal justification they were trying for was very different.

Yes, Flavio's anger is understandable. Yes, the twin diffuser goes against what the regs were trying to achieve. No, Brawn's FOTA position is not untenable.