Nico Rosberg's brilliant triumph in the Monaco Grand Prix was marred slightly when Red Bull and Ferrari lodged official protests afterwards, seeking clarification of a so-called secret test that Mercedes had undertaken with tyre supplier Pirelli after the Spanish GP earlier this month. There, the silver cars started from the front row of the grid but could not better sixth and 12th places in the race because of very high tyre wear.
While they were not protesting against the race result, Red Bull and Ferrari believe that Mercedes were given an unfair advantage for this weekend.
The Red Bull team principal, Christian Horner, whose own team were accused of subterfuge in Germany last year when a ride height adjuster was discovered on their RB8, said Mercedes and Pirelli had shown a lack of transparency, though Pirelli claimed that Red Bull were invited initially to do the test.
Immediately after the race in Monaco, Red Bull and Ferrari lodged protest documentation with stewards Lars Osterlind, Jose Abed, Tom Kristensen and Christian Calmes, alleging breach of Article 22.4h of the FIA Formula One Sporting Regulations. Meetings were convened to hear representations from the two teams, and Pirelli.
Later on last night, the FIA issued a statement which said that it only sanctioned the use of a 2013 Formula One chassis at the recent Mercedes tyre test if Pirelli ran the car, and if every team was offered the same opportunity to take part.
The stewards are preparing a report, which will be sent to the governing body, and the FIA issued a statement that appeared to counter claims made by Mercedes.
The team said they had received confirmation from the governing body, but the latter suggests there were conditions attached to its approval.
The FIA said it was asked by Pirelli at the beginning of May whether it was possible for a team to test using a current car.
"Within the contract Pirelli has with the FIA as single supplier, there is provision for them to carry out up to 1,000km of testing with any team – provided every team is offered the opportunity to do so," the FIA said in its statement.
"Pirelli and Mercedes-AMG were advised by the FIA that such a development test could be possible if carried out by Pirelli, as opposed to the team that would provide the car and driver, and that such tests would be conditional upon every team being given the same opportunity to test in order to ensure full sporting equity."
The FIA also said that it had received no further information about the test, or confirmation that all teams had been given the same opportunity to take part.
Earlier in the day, Pirelli's motor sport director, Paul Hembery, said that other teams had been asked to take part in such a test before, but that Mercedes were the first to accept.
"We've done it before with another team and we've asked another team to do some work as well," he said.
The Mercedes team principal, Ross Brawn, said that Pirelli had requested other teams help out but that none had been willing to do so.
"Pirelli has been asking teams to help them out for 12 months and people haven't been supporting them," Brawn said. "There are lots of communications between Pirelli and teams asking them to do 1,000km for them, and we obviously had an issue in Bahrain with Lewis [Hamilton] which we were quite anxious about – and we made the effort to help them. Nobody else seems to have done that."
The matter will now be considered by the FIA before any action is decided upon.