Running a smaller rear wing configuration enabled Max Verstappen to enjoy a straight-line speed advantage over Mercedes across the weekend and helped him defeat Lewis Hamilton in the closing stages of the race to take his third victory of the season.

After the Paul Ricard race, both Hamilton and Mercedes team principal Toto Wolff suggested that Red Bull’s performance had been boosted by a Honda engine upgrade, with both Red Bull and sister squad AlphaTauri moving onto their second power unit of the year in France.

Wolff said: “They have made a huge step forward with their power unit, introduction of the second power unit, and their race car is good, no doubt about that.”

F1’s rules state that teams must run the same-spec power unit throughout the season with an engine homologation period in place until 2022.

As a result, Horner has been left baffled by the remarks coming from the Mercedes camp.

"We're not allowed to make progress,” he responded when asked about Wolff’s comments. "I don't know what he's referencing there.

"I think that it's the same specification as the first unit. We've run a much smaller rear wing, so that's why the straight line performance was strong.

"I think Honda are doing a great job, but we don't see a sudden significant increase in power.”

And Horner believes Red Bull’s victory in France was the perfect response to disprove recent accusations relating to how the team was running its tyres and rear wing.

“A lot of comments have been made in the last few weeks, accusations made,” he added.

“But we comply with the rules and the way that we reacted, I think, again, it shows the strength and depth, that our performance isn’t based on rear wing flexibility and at all times we’ve always followed the prescriptions from Pirelli.

“Obviously the increase in tyre pressure this weekend was challenging for all the teams. But again, the engineering team have done a great job in optimising the car around it.”