Red Bull and AlphaTauri are on the search for new engines after Honda announced it will leave Formula 1 at the end of 2021.

The Japanese manufacturer returned to the grid back in 2015, teaming up with McLaren, but would embark on three difficult years with the British team dogged by poor performance and reliability.

Parting ways at the end of 2017, Honda found a lifeline at Toro Rosso to continue their F1 project and their improvements that season tempted Red Bull to split with Renault and partner with them for 2019.

Across the two teams, Honda has enjoyed five wins and one pole over the past two seasons.

But in a statement explained the decision had been made to leave the sport to focus on other power sources, such as fuel cell vehicles and electric vehicles as part of their push to be carbon neutral by 2050.

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Responding to Honda's decision, Red Bull boss Christian Horner said: “As a team, we understand how difficult it has been for Honda Motor Company to reach the decision to step back from Formula One at the end of the 2021 season.

"The shifting focus within the automotive industry has led to Honda’s decision to re-deploy their resources and we understand and respect the reasoning behind this. Their decision presents obvious challenges for us as a team but we have been here before and with our strength in depth we are well prepared and equipped to respond effectively, as we have proven in the past.

“Whilst we are disappointed not to continue our partnership with Honda, we are enormously proud of our joint success, delivering five wins and 15 podiums for both Red Bull-owned teams and we thank everyone at Honda for their extraordinary efforts and commitment," he added.

“Our joint focus for the remainder of the 2020 and 2021 seasons are unchanged, to fight for victories and challenge for the championship.

"As a signatory to Formula One’s latest Concorde Agreement, Red Bull Racing remains committed to the sport in the long term and we look forward to embarking on a new era of innovation, development and success. As a group, we will now take the time afforded to us to further evaluate and find the most competitive power unit solution for 2022 and beyond.”

Under the current regulations, Renault would be obliged to re-partner with Red Bull and AlphaTauri in 2022 as the French manufacturer will have no customers after this year.