Christian Horner has revealed a "heated exchange" with Formula 1 rival Toto Wolff took place at the 2021 British Grand Prix.
At the Silverstone event, Horner's driver Max Verstappen started on pole with Wolff's Mercedes driver Lewis Hamilton second.
Approaching Copse on the first lap, Hamilton ducked to the inside of the fast-right hander, but he and Verstappen collided - pitching the Red Bull into the barrier with an impact of over 50g.
Hamilton was given a time penalty, but still won as Verstappen was taken for precautionary checks in hospital.
It was the first on-track flashpoint between the two title rivals - with Horner saying it also boiled over between the two team principals.
Horner vs Wolff
Prior to the British GP, it had been a rather cordial championship battle between the two teams, although Red Bull were adamant Hamilton should have received a harsher penalty - with former International Formula 3000 driver Horner saying the seven-time Formula 1 World Champion drove "like an amateur."
The two drivers would also collide in Italy and in Saudi Arabia before the controversial ending to the Abu Dhabi Grand Prix - but Silverstone was where things finally boiled over.
"It really permeated at Silverstone where suddenly there was an awful lot of dialogue from Toto to [then race director] Michael [Masi]," Horner told Tom Clarkson on the F1: Beyond the Grid podcast.
"Then he's (Wolff) sending him an email, and then he's coming up. And I thought: 'Right, okay, I'm not having that, I'm going up.' B
"I felt it was incredibly one sided that a team principal should not be able to lobby and influence the race director and with hindsight, Toto and I had a fairly heated exchange in Race Control.
"At that event, where Toto was obviously arguing his corner that his driver shouldn't be penalised, and I've got a driver in hospital and the car taken out of the race and was obviously feeling pretty aggrieved by it."
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Horner regrets pushing for team radio to FIA
Horner also admitted that he was one of the big pushers behind introducing the FIA-pit-wall team radio that featured in 2021, debuting at the Spanish Grand Prix.
However, both Wolff and Horner used it throughout the season to lobby Masi - evident in the season-finale in Abu Dhabi.
But while he regrets pushing for it, Horner does not believe it had an impact on Masi's decision-making behind the safety car in the 2021 finale.
"I was probably guilty, because I was pushing for it within the strategy meetings and commission meetings to say that 'There's an awful lot of intercom that goes on, that I think the spectators should be aware of.'
"That's mainly between the team managers and the referee, and, the result of that is that hopefully, he may get less of it, but I think it'd be a fascinating exchange, because the team manager is only going to call up the race director, if they feel they've got something really strong to argue they're not going to bitch about something that's fairly trivial.
"And it was in Barcelona that Sunday, I hear they broadcast Toto on the phone to Michael, I thought: 'That's a bit strange. I never had a one to one channel, it always been sent it through our team manager.'
"After that race, I think we should have said: 'Right, you know what, there should only be one communication between the race director and team managers.'
"At that point, the competitiveness, you become so driven, that it's only natural, you're going to do the best that you can for your team.
"I guess that came to no greater head in Abu Dhabi, where Toto at several points during the race was trying to not get a Safety Car, they didn't want us trying to steer the course of the race.
"As soon as you hear that, because I get that transmission, My immediate reaction is, defence, I want to make sure my best form of defence is attack to say because the worst thing is last person in somebody's ear has the greatest influence.
"I think that the key factor was [Nicholas] Latifi crashing, and there being a relatively straightforward Safety Car with an amount of laps left, with a priority of being let's get the race going again.
"The only mistake made was not to let the two final cars unlap themselves - it would not have made an ounce of difference, the outcome would have been identical to what happened."
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