The decision, foreshadowed by McLaren executive director Zak Brown in June after months of internal tension, comes just three years into the 10-year supply agreement.
The split follows Toro Rosso’s agreement to partner with Honda for 2018, which frees its current Renault engine supply to power McLaren next season.
Negotiations to ensure McLaren a new engine have been fraught, with a temporary breakdown in talks between Toro Rosso and Honda in August putting the deal in jeopardy.
When discussion resumed several weeks later, Renault presented a further obstacle by demanding Toro Rosso release Carlos Sainz in exchange for its agreement to end its engine contract with the Red Bull-owned team early.
Renault is understood to have signed a contract with Carlos Sainz on the weekend after the Italian Grand Prix, with the Spaniard set to replace Jolyon Palmer at the French team next season and perhaps as early as the Malaysian Grand Prix.
Pierre Gasly, 2016 GP2 champion, will replace Sainz in either scenario.
With the stars aligned, McLaren, Honda, Renault and Toro Rosso are expected to make their respective announcements ahead of the Singapore Grand Prix on Sunday (Sept 17).
For the Red Bull, Toro Rosso’s owner, the deal represents Red Bull Racing with an opportunity to become a works team with Honda should the Japanese manufacturer come good in the low-pressure environment of its junior team.
Renault’s switch to supplying McLaren wins it a high-profile customer and Carlos Sainz, who it has long sought to pry from Toro Rosso, as a bonus.
For McLaren, however, its abandonment of Honda in favour of Renault represents a multi-million-dollar gamble, primarily at the behest of star driver Fernando Alonso.
Honda’s involvement with McLaren, comprising sponsorship, free engines and driver salary contributions, can be calculated at in excess of US$100 million (B3.31 billion). Compounding that figure further is the team’s loss of sponsorship revenue after five years of competitive decline, three of which have been in partnership with Honda, and the corresponding loss of prize money due to poor results.
With McLaren now set to foot the bill for Renault engines – on 2017 form the least competitive and most unreliable after Honda – and cover the expense of re-signing the out-of-contract Alonso, its competitive target for 2018 must be set no lower than podiums and race victories.
After all, with Alonso playing chief motivator in the team’s quest for an alternative power unit as he searches for a third world title in the twilight of his career, anything less could see the mercurial Spaniard walk from Woking for more competitive pastures anyway, leaving McLaren having upended its entire sporting framework at enormous cost for nothing.
Worse, with its chief rivals now fellow Renault customer Red Bull Racing and the Renault works team itself, its performances – and any slip-ups – will be judged harshly, further battering its reputation.
If McLaren has forged a path back to the front of the grid, it is a narrow one. The championship-winning future it ordained for itself and Alonso could yet be realised, but the stakes in attaining it have been multiplied exponentially.
This week could prove a defining one in the history of Formula One’s second most successful team.