Ahead of the Singapore Grand Prix it emerged that two F1 teams may have breached the $145m spending limit imposed for last year, when Red Bull’s Max Verstappen beat Lewis Hamilton to the world championship in a controversial conclusion to the season following a mishandled Safety Car period. 

The FIA are set to issue certificates of compliance with the 2021 financial regulations on October 5, when it will be revealed officially if teams have confirmed to the financial regulations or not. 

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On Friday evening in Singapore Mercedes boss Toto Wolff claimed one team was “massively over” the 2021 budget cap, though he stopped short of publicly naming Red Bull, despite some heavy suggesting. 

Ferrari agreed it is an “open secret” in the F1 paddock that violations of the cost cap have occurred and called for “maximum penalties” for any team found guilty of such infringements. 

Horner, who expressed confidence in his side’s submission, hit back at the accusations coming from rival teams as being “bang out of order”. 

“We were a little bit taken aback by comments that were coming from two of our rival teams yesterday,” Horner said on Saturday morning. 

“The submission between the team and the FIA is one that is confidential. I have no idea what the outcome of our rivals’ submissions are, or the accounting treatment or so on. 

“So I would be intrigued to know where their source of information for these fictitious claims have come from. They are hugely defamatory and we take umbrage to them.

“How on earth do they have this information? Where do they have this knowledge? The FIA have even stated they haven’t even completed their process. 

“So unless there is a clear withdrawal of those statements, we will taking it incredibly seriously and looking at what the options available to us are, because it is absolutely unacceptable to be making comments of the type that were made yesterday, that is totally defamatory to the team, to the brands, and even to F1.” 

Horner accused his rivals of “underhand tactics” against Red Bull on a weekend Verstappen could win a second world title. 

“We don’t even know if we’re in breach, we don’t even know until next week, until the process has been completed,” Horner added. 

“So perhaps when these accusations are made, people in glass houses shouldn’t throw stones and we take umbrage and extremely seriously the remarks that have been made. 

“Is it any coincidence that Max has his first shot at winning a world title and here we are talking nothing but cost caps, rather than the phenomenal performance that he has had this year. 

“I think it’s an underhand tactic that’s been employed to detract from perhaps a lack of performance on track this year. 

“And of course when references are made to last year, this year, next year, we’re going to take that extremely seriously. 

“So this is an issue for the FIA to deal with but also an issue for Red Bull to consider what our position is with those comments that have been made.”