In an emotionally-charged press conference at the United Sates GP - Horner's first media briefing since Red Bull were accused of a 'minor' breach of F1's $145m spending limit during Max Verstappen's title-winning season - there was no confirmation of a punishment or details of "productive" talks with the FIA, but Horner passionately defended his team.

The Red Bull team principal, sitting alongside Brown, took particular offence to the McLaren CEO's letter to the FIA last week, seen by Sky Sports, in which he said breaching the cost cap "constitutes cheating".

Horner claimed employees' children were being bullied as a result of the allegations.

"It's tremendously disappointing," said Horner. "It's absolutely shocking that another competitor, without the facts, without the details can be making that kind of accusation.

"We've been on trial because of public opinion since Singapore [when reports of Red Bull breach emerged]. The rhetoric of cheats, that we've had this enormous benefit, and numbers have been put out by the media that are miles out of reality.

"The damage that does to the brand, to our partners, to our drivers, to our workforce... in an age when mental health is prevalent we're seeing significant issues within our workforce. We're seeing kids that are being bullied in playgrounds, employees' children.

"You cannot go around just making that kind of allegation from any fact or substance. We absolutely are appalled at the behaviour of some of our competitors."

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Horner added to Sky Sports F1: "We should be talking about Verstappen [who has won last two titles].

"Not one question has been about Max's performance, and I think it's in the interests of everybody. What's particularly disappointing is the reaction by some of our competitors, that are making massive accusations that have zero substance to them, and trying to leverage and pressure the FIA for their own competitive gain. "

In response, Brown defended his letter, which didn't mention Red Bull by name but was sent soon after their breach was revealed.

"My letter set out that if a team spent more than the cap, they're going to gain an advantage," he said. "We're not taking a view if they did or didn't. My letter was if someone has, these are the things that should be addressed.

"I didn't mention any team, it was a general response now that we are into the cost cap era, here's what we think the ramifications are."

Horner, however, claimed that Brown had a "very convenient memory of the letter that he wrote".

"We've been tried and subjected to three weeks of effective abuse," he insisted. "It's just not right. This has to stop."

Horner also batted back claims that Red Bull could have had a benefit from overspending, which Sky Sports understands the FIA have down as around $1.8m. It is also believed that Red Bull's initial submission was $4.5m under the cap, but unexpected extra costs - such as unused spare parts for their car - put them over.

"You've got to look at the relevant costs [within the cap] what's in the costs and what is out," Horner said. "Our view is that our relevant costs are within the costs.

"We are in discussions with the FIA about what the costs are and what are mitigating potential circumstances.

"We had zero benefit from a development perspective or operational perspective either from 2021 or 2022 from the way we operated within the cap. Our submission was significantly below the cap.

"We absolutely and categorically don't feel we've had any advantage either in 2021 or 22 or 23, 24. Some teams are even talking about 2026. It's totally fictitious."

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The FIA has offered terms of an 'accepted breach agreement' [ABA] to Red Bull, which would see the team admit wrongdoing but also likely receive a less severe punishment.

A fine and a reduction in future wind tunnel use has been mooted.

Horner and FIA president Mohammed Ben Sulayem held talks in the Circuit of the Americas paddock on Friday but as yet there is no development. Horner, who said he wants to be fully transparent on the process but is unable to be right now, is still hopeful there could be an agreement this weekend.

"The process, as per the regulation, is that we've been invited to enter into an ABA which is for a minor breach, that you have the opportunity to discuss with the FIA and present your case, your position on this.

"We're in that process and have been for the last and have been for the last 10 days or so, going backwards and forwards with the FIA.

"I hoped for it to be resolved before the weekend, I'm hoping it's resolved during the weekend. Should that not happen, the next process is the cost cap adjudication panel and after that the International Court of Appeals. It could draw it out another six, nine months, which is not what we want - we want closure on 2021.

"We've had healthy and productive discussions with the FIA and I'm hopeful of being able to reach an agreement in the near future.

"It's in the interest of everybody, for the sport, to get this situation resolved as soon as possible. And I think there are many lessons to be learned from it."

One of those lessons, Horner says, is on communication - and what is included as a cost in the spending limit. The cost cap was new for 2021.

"We expected certain things to be potentially challenged or clarified," he explained.

"It's a new process. We made an interim submission in 2021, there was no feedback or suggestion we were doing anything that was contrary to any regulations.

"Then of course the submission made in March, again we didn't hear anything from that until the latter part of September. There's also duty from the regulations to guide to have effective compliance."

He continued: "Unused inventory treated [in the cap] was in our view a change to the regulation... a clarification came out in June that changed the application of that, that had a seven-digit effect on our submission.

"Of course, retrospectively we were not allowed to change the submission."