Renault claims to have found a significant increase in performance from their new engine for 2019, McLaren says.

The French manufacturer revealed in October they would be developing an all-new power unit for next year having struggled to make major progress with the concept used this season.

Their biggest problem was in qualifying, with Renault reporting a 50 horsepower deficit to Mercedes and Ferrari and by the end of the year, Honda was even thought to be on a par if not ahead.

"They are telling us that they are very pleased with their winter progress," CEO Zak Brown told Autosport.

"They have found a lot of kilowatts [power], and think they will be in the ballpark."

Of course, for Renault, there is now the added motivation of proving Red Bull wrong for their decision to change to Honda from next season after four years of criticism during the hybrid era.

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Meanwhile, at McLaren, the focus is on rebuilding following a tough season which ended with the team battling with Williams at the back of the grid.

"There is a lot of cautious optimism, but we clearly don't want to get ahead of ourselves, we have done that before and we are not going to make the same mistake twice," Brown continued.

"So it is a very head down approach. Development is going well, and we are on track with what we are wanting to achieve.

"Ultimately we have no idea where the competition is, other than speculating. Everyone plants their different stories: they either want to underplay it or overplay it. I don't think we will obviously know until we get to Barcelona [for pre-season testing].

"We are pleased with the progress we have made. We have done things differently, everyone is working well together, so it feels like a quiet confidence.

"But we are on our toes. We know this is an important year for us to show progress and that comes with some exciting nervous energy."