Renault will not begin spending its allocated power unit tokens until the final rounds of the 2015 Formula 1 season as it continues to focus on improving reliability.

Following the decision to introduce upgrade tokens as a compromise to a partial 'unfreezing' of the engine regulations, Renault began the year with 12 of its allocated 30 tokens still available to use over the course of the 2015 season.

However, whilst Ferrari and Honda have spent tokens since then, Renault is yet to delve into its allocation to update its much maligned power unit, which has struggled for pace and reliability compared to Mercedes.

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Nevertheless, Red Bull Racing boss Christian Horner says Renault will continue to withhold the tokens until the final portion of the 2015 season, most likely the Russian Grand Prix in Sochi.

"I don't think there is anything scheduled now before Sochi," he said. "That probably is the earliest that we are going to see any form of development or use of the tokens, so the engines we've got at the moment are what we're having to live with for the time being."

It means Red Bull is once again facing grid penalties as the current engines are forced to go long without any updates, a threat evidenced by Daniel Ricciardo's engine blow during the Hungarian Grand Prix FP2 session.

"So engines four and five of what the drivers have been using between Friday and Sunday racing, unfortunately Ricciardo has now lost engine four, so he's only got engine five, that came into service for the first time in Austria, to get him through the next few races.

"Only time will tell as to whether we can get to Sochi or not without incurring another penalty before introducing an upgraded unit."

Ricciardo escaped punishment for his FP2 engine blow as he was using a 'practice engine' and not a race engine.