Red Bull Formula One team boss Christian Horner attended a hearing on Friday to answer allegations about his conduct that have cast doubt on his future and could overshadow the champions’ car launch next week.

Red Bull Racing and the Austrian energy drink parent company, who have not detailed the nature of the complaint, remained tight-lipped with representatives not responding to calls or emails.

F1 insiders said they understood the hearing was held in London at an undisclosed location rather than the team’s Milton Keynes factory.

Sky Sports television reported the meeting with an independent barrister lasted almost eight hours.

One informed source said that Briton Horner, 50, denied the allegations ‘in the strongest possible terms’ at a meeting this week of the Formula One Commission.

Sources cautioned there might not be any outcome until after the scheduled car launch next Thursday, with the barrister possibly needing to carry out further hearings.

Former F1 supremo Bernie Ecclestone said he spoke to Horner on Thursday evening.

The pair have been close for years and Horner, who is married to former Spice Girls singer Geri Halliwell, was best man at Ecclestone’s wedding to his Brazilian third wife Fabiana Flosi in 2012.

Ecclestone was also close to Red Bull’s late co-owner Dietrich Mateschitz.

“I spoke to him yesterday and it was the normal Bernie and Christian conversation about things in general,” he said. “We had a chat about what’s going on in the sport.”

Red Bull Austria said in a statement on Monday that they were investigating a complaint against Horner, without saying where it came from or what it was about.

“After being made aware of certain recent allegations, the company launched an independent investigation,” it said.

“This process, which is already underway, is being carried out by an external specialist barrister. The company takes these matters extremely seriously.”

The BBC and Sky Sports television said they understood the complaint was related to inappropriate behaviour of a controlling nature towards a female member of staff.

Red Bull are due to launch their 2024 car at the Milton Keynes factory, an event that will also celebrate the team’s 20th season. Horner and his team celebrated the most dominant season in Formula One history last year, with Red Bull winning 21 of 22 races.