Brackley-based Mercedes are at an FIA tribunal in connection with their controversial Pirelli tyre test.
Mercedes' defence rests heavily on their assertion that they were given permission by FIA race director Charlie Whiting to use their current 2013 car at the test.
However, Mark Howard QC, speaking first on behalf of the FIA as the body's legal representative, said Whiting's consent was "irrelevant".
Howard said that Whiting was not authorised to amend Article 22 of the sporting regulations - which covers the ban on in-season testing - saying such a move could only be undertaken by the FIA's World Motor Sport Council.
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Some sharp showers will develop this afternoon and it will continue to feel unseasonably cool
The familiar chimes of the Luton Town Hall clock are now silent for a few months while it receives a major overhaul.
Most places in the Anglia region will have a dry start with some sunshine. A few showers will develop and these could become heavy.