Berliner Tageblatt - Mercedes take detour for 'secret' test day in France

Widespread reports of a test behind closed doors on Thursday followed the publication of a photo of George Russell at the wheel of the car on Mercedes' social media channels as the team bids to recover form after a disappointing start to the season.

Teams are allowed two official filming days per season, during which they are not prohibited from testing new parts.

Wednesday's day at the Le Castellet circuit, home of the French Grand Prix, was a convenient stop for the team en route to Catalonia.

The team did not comment on, or deny, the reports and did not confirm if or what parts of the long-awaited upgrade package were being tested.

It is not uncommon for teams to use filming days to test parts as well as to provide content for commercial partners – Ferrari took part in a similar activity at Monza last Friday with championship leader Charles Leclerc driving their car.

Mercedes were reported to have tested a new rear wing configuration and an updated power unit in a bid to improve their straight-line speed and reduce the effects of 'porpoising' that have been such a problem with the new 'ground effect' cars.

Russell had complained earlier this year of the effects of the 'bouncing' of the car and said he had suffered severe back pains, but he has remained faithful to the potential of the new car.

"I think we can find chunks of time once we find the key to unlock the potential of the car," he said. "We have to keep pushing and it will come, I believe."

The unpredictable nature of the car's performance, which changes acutely with variations in conditions and set-up, has undermined the team's title defence and seen Leclerc top the drivers' championship ahead of defending champion Max Verstappen of Red Bull.

F.Müller--BTB