Red Bull felt ‘reluctance’ from Renault in Formula 1

Talk that Renault wanted to move beyond its engine supplier role and run its own team for a third time surfaced early in the 2015 season, and Horner believes those intentions influenced its relationship with Red Bull.

"I never felt that Renault fully embraced the technical capability and simulation capability that we tried to offer and it was very clear early on that Renault weren't happy just being a supplier," he said.

"From the back end of last year they'd been looking at becoming an entrant again."

Dissatisfied with the performance and progress of Renault's F1 power unit project, Red Bull brought in Ilmor chief Mario Illien and set up its own engine group to try to assist.

Ilmor will continue working with Renault as it takes over Lotus to relaunch its factory F1 team next year, but Horner said the French firm had initially been against Illien being involved.

"Renault went through some management changes towards the end of last year and there was an awful lot of talk going on," said Horner.

"We introduced Mario Illien to them. There was resistance to using Mario initially.

"We created an engine group to support. There was not the smoothest of relationships between Milton Keynes and Viry, and out of that obviously grew frustration.

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

"Mario developed a concept for Renault and Renault, in parallel, ran their own projects - the outcome of which was the D-spec.

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

With concerted efforts to secure an alternative engine supply having all failed, Red Bull will continue with Renault next season after all, but running TAG Heuer-badged V6s in a restructured deal.