Mercedes' plans to appeal Nico Rosberg's 10-second time penalty at the British Grand Prix look set to tee up a test case for Formula 1's ongoing controversy over team radio communication.

After a push by teams last week to try to free up the restrictions to let them tell drivers more, the FIA responded on the eve of the Silverstone weekend by telling them that actually the situation was going to get tougher.

For rather than any move to ease back on the desire to make sure drivers drive the car alone and unaided, the FIA said that from now on teams would be reported to the stewards for breaches of the rules, rather than have F1 race director Charlie Whiting have a quiet word in their ear.

As Williams technical chief Pat Symonds said of the new FIA position: "The honeymoon period is over."

The Mercedes case

The Rosberg situation revolves around messages that were told to Rosberg by the pitwall when his car got stuck in seventh gear six laps from the end of the race.

The radio conversation went like this:

Rosberg: "Gearbox problem."

Engineer: "Driver default 1-0-1, chassis default 0-1, chassis default 0-1."

Engineer: "Avoid seventh gear, Nico, avoid seventh gear."

Rosberg: "What does that mean, I have to shift through it?"

Engineer: "Affirm Nico, you need to shift through it. Affirm, you need to shift through it."

From Mercedes' perspective, it felt that its words to Rosberg were within the regulations, as the rules do allow teams to help in relation to a potential critical failure of the car.

The FIA and the stewards came to the conclusion, however, that while some of that conversation was indeed okay in sorting out a 'critical' problem, the second part of the instructions went too far in helping Rosberg drive the car.

What the rules say

Such an allowance for helping in critical situations is made in Technical Directive 014-16, which was issued by the FIA to teams in April. It is the most up-to-date reference point of the radio rules.

The document is a list of all the types of permitted messages that teams can issue at all times the car is out of the garage with the engine running and the driver on board.

The Mercedes case revolves around Article 2 of this list. It states that teams can give the following message.

"Indication of a critical problem with the car, any message of this sort may only be used if failure of a component or system is imminent and potentially terminal."

From Mercedes' perspective, it was this clause that was highlighted as justification for the radio messages, and it was why it was read out by team boss Toto Wolff after the race.

"In my opinion, that was the basis of our decision and now the FIA stewards have to judge," he said prior to the hearing.

Wolff admitted that there had been a small debate on the pit wall about what the team could or could not tell Rosberg, but it quickly concluded that without the instructions Rosberg was going to retire.

"It would have been stuck in seventh gear and that would have been the end probably," explained Wolff.

Indeed, the stewards accepted that some of the instructions – especially those that helped Rosberg keep his car running – were allowed.

Performance boost

However, while agreeing that the team's changing of setting advice was okay, it is understood it felt the messages about not using seventh gear went too far.

Indeed, the car would happily have run – albeit in a slower state – without that advice and it could be argued that by being told not to use seventh gear (and how not to use it) it helped boost its performance.

Article 4 of the allowed radio rules states clearly: "Any new setting chosen in this way must not enhance the performance of the car beyond that prior to the loss of function."

Mercedes does not buy that its gear change comments delivered a performance boost though, and it well knows after Baku and LewisHamilton's radio dramas there about where the lines are drawn.

Wolff added: "Like we had in Baku, when you have a problem on the car and performance is not like it should have been, but the car can go the end, you are not allowed to say that.

"But in this case, you cannot make your way around stuck in seventh gear. That is the end."

Legal precedent

If Mercedes sees through with the radio appeal then it will open the way for a proper open debate – and legal precedent – on just what is and is not allowed.

Some teams, for example, have interpreted the Article 2 clause as simply being an allowance for teams to notify their drivers of an imminent critical failure, and not actually as a clause that allows them to tell drivers how to fix it.

Indeed, there appears to be some uncertainty about why Force India said it was not allowed to warn Sergio Perez of an imminent brake failure in Austria a week ago, but Mercedes could help Rosberg overcome a gearbox problem.

Mercedes (which also had brake trouble in Austria) thinks that such uncertainty needs clearing up, and it may be the real motivation as to why Wolff may want to take it all the way to the FIA Court of Appeal.

"It [the brakes issue] was a discussion we had last week [in Austria]," added Wolff. "We said we are about to have a failure. We want to communicate it and couldn't.

"So we can see that the rules maybe need a rethink, and try to keep it between the FIA and the teams to maybe go into more detail about what is allowed and not.

"Because not communicating at all, you can just plug the radio out and throw it out of the car. I think this is part of driving since a long time, but it needs to be discussed."

The frustration felt inside Mercedes about the situation is clear, and all eyes will now be on whether it choose to go through with its appeal.

As Mercedes powertrain engineer Tommy Batch tweeted on Sunday night, the implications of what Rosberg being told as being illegal go far beyond just Silverstone.


Gallery: Analysis: British GP controversy a defining moment for F1's radio rules