After struggling to a disappointing seventh-place finish in last year’s constructors’ championship, Aston Martin completed a remarkable transformation over the winter to emerge as Red Bull’s nearest challengers at the start of 2023. 

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Fernando Alonso has completed the podium behind the dominant Red Bulls on four occasions this season, while he finished runner-up to Max Verstappen in Monaco to claim his and the team’s best result so far. 

Despite Mercedes’ recent resurgence, which saw them leapfrog Aston Martin into second place in the constructors’ standings at the Spanish Grand Prix, Horner still sees Aston Martin as Red Bull’s biggest long-term threat. 

“We have a lot less wind-tunnel time than you guys,” he told Aston Martin ambassador Pedro De la Rosa when speaking to DAZN.

“So we’re having to be very selective about how we use that time, and also thinking about next year as well – so it’s about finding that balance.

“When you look at all that experience, you can see what Fernando’s brought to Aston Martin – which is still a young team.

“There are lots of new guys there; they took a few guys from us.

“For us, I think the team that we’re most keeping an eye on for the future is the Aston team – because you can see they have a strong energy.”

Following Mercedes’ double podium finish in Barcelona, Horner delivered a brutal reminder of the work the German manufacturer still needs to do to catch Red Bull. 

When asked by Sky whether Mercedes will become a concern for Red Bull, Horner answered: "It was still 23 seconds behind at the end of the race. They made a good step, but we've got some stuff in the pipeline.”