Mercedes' highly-anticipated 2012 car made its track debut this week during a secret test day at Silverstone.

"Lots of questions about Silverstone and shakedowns," admitted the Northamptonshire based team on Twitter on Thursday.

Youtube video footage, captured by a trackside observer, showed the 'step' nose W03 turning laps at the British grand prix venue, which is located just a 15-minute drive from the German team's Brackley headquarters.

Mercedes said the test was for "filming" purposes, with Nico Rosberg and Michael Schumacher's equally sharing the allowed 100 kilometres of running.

Italy's Autosprint website said the car appeared "fairly conventional", despite speculation the late test debut is due to the team keeping an explosive technical innovation close to its chest.

Adrian Newey, Red Bull's car designer, admitted he and Mercedes' rivals might have a very close look at the W03 if the rumours about the technical secret are true.

"If it comes out and goes three seconds quicker than anybody else, yes of course," he is quoted by Reuters.

"Other than that, simply because its later doesn't mean to say you are going to suddenly show more attention at that than anybody else's."

Meanwhile, after the struggling Spanish team's 2012 car recently failed two mandatory FIA crash tests, HRT will sit out next week's Barcelona test.

Last week at Jerez, Pedro de la Rosa ran at the wheel of the 2011 car.