The Mercedes F1 team has raised hackles amongst rivals in Monaco after it emerged that the Brackley team had carried out three days of tyre testing immediately after the Spanish Grand Prix.

Mercedes has struggled more than most with tyre wear problems on its W04, and has seen three straight pole positions squandered with poor race performances due to them. Although Lewis Hamilton turned pole into third place in China and Nico Rosberg salvaged sixth from top spot in Spain last time out, the Briton was lapped after starting alongside Rosberg on the front row in Barcelona.

Now, according to reports emanating from paddock in Monaco, it appears that the Brackley-based team may have been able to work on possible solutions to its problems during an FIA-sanctioned outing at the Circuit de Catalunya that somehow got around the regulations banning in-season testing.

Article 22 of the F1 sporting regulations governs testing, and clause 22.4 setting out the restrictions placed on teams. Despite that, it appears that Pirelli is allowed to run with one team during the season outside of those rules, and chose Mercedes to carry out the job of evaluating potential tyres for next season immediately after the Spanish Grand Prix. It is claimed, however, that Pirelli also used the test, which featured both Hamilton and Rosberg, to run the tyre it intends to take to the Canadian Grand Prix next month, in response to concerns about the safety of its existing rubber.

As expected, disclosure of the test has rival teams up in arms, with Red Bull and Ferrari already thought to be considering a protest having not been informed that the test was taking place.

"We found out second-hand last night," RBR team principal Christian Horner told journalists, "I think there's confusion between what is contractually permissible and what isn't, and what a team - when it enters the world championship - is allowed to do within the sporting regs. It's a situation that we need clarification on, and our position is that we are going to request that clarification.

"I can understand Pirelli wanting to test the tyres - they've obviously got issues with the tyres. What's disappointing is that it's been done in not a transparent manner. A three-day test has taken place running a current car on tyres that are going to be used in the next grand prix. Irrelevant what you call it, that's testing. [Mercedes has] got both cars on the front of the grid, so it's not hurt."

Horner confirmed that a chat with the authorities was in the pipeline.

"First of all, we need to deal with it through the proper channels, so that's what we'll look at doing," he said.