On the back of a difficult campaign for the Red Bull and Renault partnership, Horner has his views as to why the French car manufacturer's decision to focus on just two teams did not pay off.

But he admits that there is not a clear answer as to why the partnership failed to repeat the results that helped it secure four back-to-back world championships from 2010 to 2013.

"To be honest, I am not entirely sure," he said, when asked by Motorsport.com about why Renault slimming down its F1 involvement to just Red Bull and Toro Rosso did not work.

"There was always a reluctance to fully embrace Red Bull as a technical partner, and there was a difference of opinion technically on where the weaknesses of the engine were.

"We couldn't influence the technical direction of the development. Mario [Illien] developed a concept for Renault, who in parallel ran their own project - the outcome of which was the D-spec.

"I never felt that Renault fully embraced the technical capability and simulation capability that we tried to offer.

"It was very clear early on that Renault were not happy being just a supplier. From the back end of last year they have been looking at becoming an entrant again."

Red Bull investment

Horner said that Red Bull devoted its own resources to try to help Renault fast track improvements, but in the end its efforts did not help.

"We invested quite a lot into creating a group, employing some specialists, making capacity available – so it is frustrating that that didn't really bring anything to fruition," he said.

Horner did concede, however, that Red Bull had pushed Renault hard with its packaging demands, something which may have contributed to power frustrations.

"Of course we pushed – but any competitive team is going to do that," he said.

"Every technical meeting, every operational meeting, if you don't push the boundaries you don't go quick in this business. That is the approach we have always taken in any single area."

When asked if Renault's conservatism ultimately held it back, Horner said: "I think in some respects, it possibly has. So it is good to hear that they are looking at a bit of a restructure."