The new MGU-K, which was once scheduled for introduction for as early as the start of the 2017 season before numerous delays, has finally been signed off for use on a race weekend by all three teams.

However, Renault F1 boss Cyril Abiteboul says that at least one the customers has preferred to stick with the old spec, at least for Austria.

One of the complications is that under the 2018 regulations drivers can use only two MGU-Ks per season, before penalties result.

McLaren and Red Bull may thus be loathe to make a switch until the new spec has been proven by the works team in race weekend conditions.

“It’s available for all the cars that want it,” Abiteboul told Motorsport.com. “It happens that not all teams have elected to go to the new spec.

“It’s one that we’ve been long awaiting, but it’s a bit of a problem that some teams have elected not to use it, which means that they will continue to use the MGU-K of a previous technical definition, with a higher reliability risk.

"But that’s our philosophy, to accept the teams’ choice, having all the information.”

The change comes immediately after works driver Carlos Sainz suffered a failure with the old spec MGU-K in the closing laps of the French GP.

“It’s a part that we know was fragile, it’s a part that we deliberately decided to extend the life of, because we knew that there was a new definition, a new spec coming up, with better performance, better packaging and with a better reliability level.

“It’s coming next weekend, but it’s two laps too late for that particular MGU-K!

"Having said that it’s not that bad, because it’s really showing that we are pushing to the limit and we are accepting to take risks.”