Mercedes and Ferrari are "working as one team these days", according to Red Bull team principal Christian Horner, as Formula 1's political battle reignited at winter testing.

Both Mercedes and Ferrari, F1's dominant teams in 2017, have raised opposition to Liberty Media's proposals for the future of F1 with Scuderia president Sergio Marchionne warning Ferrari could quit the sport unless the plans are redrawn.

Speaking on the first day of pre-season testing, Mercedes boss Wolff told Sky Sports that many of Marchionne's comments "make absolute sense".

Told of the remarks, Red Bull chief Horner responded: "Mercedes and Ferrari are working as one team these days.

"Sometimes it is difficult to tell which is which. For the last couple of years there has been a very tight relationship between Ferrari and Mercedes. They even broadcast each other's launches and things like that these days."

McLaren have called on Liberty Media to finalise their plans for the sport regardless of the threats of a revolt and a concurring Horner says F1's new owners must take control of F1's destiny.

"We are focused on going racing, things that we can control, there are new owners in Formula 1 in Liberty and they have to decide what they want Formula 1 to look like moving forwards.

"I'm sure they will lay out their roadmap and plan during the course of this season and we will go from there. But of course there is going to be a lot of posturing and positioning and you can see that has already started in certain quarters."

How real is the threat of a breakaway?

On the eve of the start of testing, former Formula 1 supremo Bernie Ecclestone suggested Ferrari could lead a breakaway series unless their demands were pacified and urged Liberty Media not to assume the Scuderia were bluffing in their threats to quit.

While Wolff has denied the world champions are considering walking out of F1, the Silver Arrows chief reserved the right to offer constructive criticism of Liberty Media's proposals.

"We are committed to Formula 1, this is our joint-platform and we all benefit if it is running well," Wolff said.

"This is what we are concentrating on, giving the management of Formula 1 and the FIA the utmost support to solve the problems, to make it great, better the show and this must be our clear No 1 priority.

"Most of the things Sergio says make absolute sense to me and this overlays with our position. We are critical on some of the things because we want Formula 1 to do well. We invest a lot in this platform, it's a major global sport that has grown over the years and we feel responsible."

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Horner also believes a rival series is unlikely.

"Bernie knows every time the Concorde came up for renewal there was talk of a different series," Horner said. "Since my involvement over the past 14 years, every time it's up for renewal, bang there is another series mooted. It hasn't happened yet and I don't think it's going to happen at the moment.

"Formula 1 is and will be the pinnacle of motorsport and it is down to the commercial rights holder and the governing body to say 'this is what the future looks like' and then it's down to the teams whether they want to be part of it or not."