Mercedes has outlined its defence against charges that it undertook an unauthorised private track test using 2013 equipment at the Circuit de Catalunya last month on the grounds that it was not they who were testing, but Pirelli.

"The only sensible conclusion is that what happened on that day, whether one calls it a test or track running, [is that it] was conducted by Pirelli," argued Paul Harris QC, the barrister appearing on behalf of Mercedes.

"The people who were present on the day all unanimously give the same evidence about what was going on, who was doing it, and who was in charge of it. It is undeniable the testing was undertaken by Pirelli.

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"If the test wasn't undertaken by Mercedes, there is no case," he added. "They are the critical words in the text of Article 22: 'undertaken by.'"

Harris also argued that the test was lawfully undertaken under clause 4.2 of Pirelli's commercial contract, which the Mercedes advocate said was not the same as the testing banned under Article 22 of the Sporting Regulations.

And Harris also revealed the much-rumoured emails from Charlie Whiting, the FIA's technical head, which the team felt gave them the leeway to participate in the test session, ostensibly as a 'third party sub-contractor' to Pirelli in the matter.

"In my view, any such testing would not actually be undertaken by the competitor," Whiting's email to FIA lawyer Sebastien Bernard reads. "Do you think we would be able to take this position to allow Pirelli to undertake a meaningful test?"

"Indeed we could take this position," Bernard replies. "[That it is] not an undertaking from the competitor [Mercedes.]"

Harris insisted before the tribunal that Mercedes had "acted in good faith throughout, conducting a test to the benefit of all F1 participants."

The Mercedes representative also raised the issue of a prior test conducted by Ferrari on behalf of Pirelli, which the FIA has decided not to pursue to a hearing as the hardware involved in that case was 2011-vintage.

Harris said that the Mercedes test in Spain in May was planned and conducted in exactly the same manner as Ferrari's earlier session, and that Whiting's approval had been sufficient in that case without raising the matter to the full World Motor Sports Council for authorisation.

If that was okay and not a breach of article 151c of the Sporting Regulations in Ferrari's case, the barrister asked, then why were the rules different now for Mercedes?

The tribunal continues at the FIA's headquarters in Place de la Concorde. The hearing is expected to finish this afternoon, although the panel's ruling might not be issued until a later date.