Mercedes were asked by Pirelli to conduct the test after Barcelona, in a move that sits outside of the Sporting Regulations and instead is part of the agreement between the tyre manufacturer and the FIA. This agreement reportedly allows Pirelli the option to request a teams involvement in the test in order to aid in their tyre development.
What should have been a one day test was hampered by poor weather, leaving the test straggling out over 3 days, with the Silver Arrows covering around 1000KMS, 900KMS more than can be conducted in any promotional event. It also raises the question of what mileage the team completed in the pre-season tests with an upper limit of 15,000KM of track testing available to teams each year (Article 22.3)
It's not yet known if Hamilton or Rosberg were at the wheel of the W04 during these test days or whether the car was passed over to Sam Bird or another test driver to conduct the tests.
The other teams are reportedly furious with the situation claiming that Mercedes will have gleaned an advantage from the situation. The question however is: What tyres did Pirelli use on the W04 during these tests? This years tyes, last years or tyres they are proposing for change in Montreal?
So is this an argument to be had in Monaco? Not for me, yes an advantage may have been passed to Mercedes but in reality the team have struggled with understanding how to manage tyres since Pirelli joined in 2010. One test is not going to resolve an issue the team have had for 3 years....
The other issue we may also find is, Pirelli stand on the precipice of walking away from Formula One, with no contract in place for 2014 and mass bickering over their product they may decide enough is enough. That would leave F1 in an extremely delicate situation with very little room to manoeuvre and realistically opening up an option that the FIA considered several years ago: Their own unmarked, unbranded tyre manufactured by a brand but purchased in by the governing body and dispensed to the teams.