The FIA has denied that it knew about or approved Mercedes' secret tyre test with Pirelli in Barcelona in May.
Arguing before the International Tribunal convened on Thursday in Paris, FIA's lawyer Mark Howard QC agreed that Pirelli had made an informal approach to the sporting body about a possible tyre test, but insisted that Pirelli had not given confirmation to the FIA that the test would take place, or communicated details about the date or location that any such test would occur.
The FIA said that the only way to overrule the sporting regulations prohibiting in-season testing would be to send those full details to the World Motor Sport Council (WMSC) for a formal decision on whether it could go ahead or not. Neither Pirelli nor Mercedes ever did so, the FIA alleges.
The FIA has now conceded that Charlie Whiting had been informally approached by Pirelli about the prospect of an in-season test, but argues that any response he gave was "only the opinion of someone within the FIA; Mr Whiting is not in any position to provide a binding statement with respect to the rules."
That would appear to torpedo Mercedes' rumoured line of defence about being in possession of emails with Whiting okaying the three-day session at the Circuit de Catalunya in the week after the Spanish Grand Prix.
The hearing has also clarified why Pirelli is being required to attend. The hearing said that it was because the test may have been "prejudicial to the competition", but that there was no question of Pirelli having breached its commercial contract with the sport.
"None of the other 2013 competitors were invited to participate in the test or observe," said Howard, explaining the seriousness of the matter. "None of the other 2013 competitors was aware that the test was to take place."
Howard said that if this was found to be the case then it amounted to a breach of article 151c of the sporting code relating to "Any fraudulent conduct or any act prejudicial to the interests of any competition or to the interests of motorsport generally."
In its opening argument, the FIA said that even if the three-day test was a 'blind' study with respect to which tyres were being run at any given time, merely being able to run an extra 1000-kilometre test would have given the team invaluable information about their 2013 car and whether or not its current problems with tyre degradation could be overcome without major revisions, or whether a significant defect was responsible for the team's race performance issues.