Gerhard Berger says Mercedes must start delivering in Formula 1

The former grand prix driver says he is 'tired' of the explanations that Mercedes-Benz has given for its failure to produce the victories or title challenges that it had predicted when it embarked on its latest adventure.

"In Belgium it was frustrating to watch [Nico] Rosberg having a hell of a start and a perfect showing, but after a couple of laps losing place after place like an apprentice driver," Berger told AUTOSPORT.

"All the explanations and excuses from Mercedes make me tired. It is high time that a premium manufacturer provides its drivers with a premium F1 car. The engine is widely regarded as the class of the field. Now it's their turn to deliver the rest."

Berger also thinks that critics should back off Mercedes GP driver Michael Schumacher, as he reckons the seven-time champion is getting all he wants from his F1 return - even if the results have not been as good as some had hoped.

"First of all I have to say that I am bored by the advice from experts that he should retire," explained Berger. "He has so much fun in racing and, with all his qualities, why shouldn't he go racing and have fun? He just combines professionalism and fun.

"After all his success he deserves this. The market has its own rules. As long as somebody gives him a car, he can do this."

Berger also thinks that Lewis Hamilton remains one of the sport's very best drivers - despite a difficult year that has seen the Briton involved in a number of controversial on-track incidents.

"Let me put this straight: I would love to have him as number one in my team if I had one," he explained. "Together with Seb [Vettel] - although maybe not, because that would not work but cause havoc!

"In my view, [Seb] Vettel, [Fernando] Alonso and Hamilton are the three best drivers out there. Vettel performs perfectly. Alonso suffers from minor mistakes, but he has not got a car on par with Seb's.

"Lewis is the best in overtaking, but with a huge amount of risk. Therefore, it's usually 50-50 if it works or if he collides. Surely, Lewis is not to blame for every collision, but he is often involved. And it does not create a nice picture if you are always there when something goes wrong."