Ross Brawn has launched a scathing attack on Mercedes saying that it is in a "vicious loop of huge budgets" which is "not really sustainable" and yields results which are "no good for the business" according to a report in American business magazine Forbes.

The caustic comments by Formula One's technical boss are all the more astonishing as they came yesterday morning just hours before Mercedes clinched a fourth consecutive Constructors' Championship at the United States Grand Prix.

Brawn, who was hired by F1's owners Liberty Media in January, has a history with Mercedes as he was boss of the team until 2013 when he left claiming that he "was beginning to deal with people who I didn't feel I could ultimately trust." He made the claim last year in his book 'Total competition, lessons in strategy from Formula 1' and it was reportedly a reference to Niki Lauda, the team's non-executive chairman, and Toto Wolff, who took over from Brawn as its boss.

However, there was no evidence that Brawn's outburst yesterday was personal as he said that the "condition" Mercedes is in is purely a result of F1's regulations.

He said "if you take the current dominant team, Mercedes, they have the biggest resources in Formula One. They spend around half a billion dollars on their Formula One programme a year to get the results they get on the track and that's a fantastic achievement. The problem is they are four seconds quicker than the guys at the back of the grid and that's no good for the business. Also it's not really sustainable.

"What happens is when they are winning, those budgets have grown. During their period of domination they spend more to stay dominant. When that domination fades away, the budgets become awkward because they are not succeeding yet they are spending a huge amount of money.

"Those teams, particularly the boards of those teams, have come to us and said 'please save us from ourselves because we have to get in that loop of achieving success. We want a regulatory authority. We want control over what we can and can't do and to make the business more sustainable. To bring the budgets down to a level that even if we are not winning we can still justify it.'

"So Mercedes, if we take an example, always want to be winning and they want to be in the top three and they are prepared to accept a reduced competitiveness if it means greater sustainability. So they are in this vicious loop now of huge budgets, having to dominate to justify the budget and looking for a way out. Not a way out of Formula One, a way out of that condition they are in."

Brawn admits that a great deal of the teams' high-octane costs are driven by the V6 engines. It is ironic he had a hand in developing them in 2010 as the chairman of the teams' Technical Working Group when he was boss of Mercedes.

As F1's former chief executive Bernie Ecclestone told Forbes, "when the current regulations were perceived, no one at the time of those putting the regulations together thought that they would result in what we have, except maybe Mercedes, as at the time, Mr Brawn was within the FIA working group and was bright enough to see the potential for Mercedes. Well done, Ross." According to Brawn, what nobody considered at the time was the cost.

"The powertrain of these cars really is very impressive but it is inordinately expensive and for the manufacturers who are running their own teams that's fine. It's all part of the package. But if you're a customer team, because a number of teams in the pitlane have to buy their engines from the suppliers, the costs are extortionate," Brawn said yesterday.

"The cost of an engine these days is about twice what it used to cost before these engines were introduced. That was never a factor that was considered when the regulations were introduced. There was a feel that we needed to get a more relevant engine - we have got a hybrid engine now - but the commercial side of it, particularly for the independent teams, was never considered properly."

Brawn revealed that a budget cap is on the horizon as F1 is "working with all the teams now to look at budget control for the future and I think that is the way forward... This creates a sustainable Formula One. The other important thing it does is it makes everyone more competitive because the difference between the guys at the front spending what they do at the moment, and the guys who are spending much less further down the grid is reduced enormously."

Brawn says at the heart of this plan will be a new engine in 2021 when the current agreements expire. In 2011 when the V6 regulations were announced by the FIA, he claimed that the engine "creates a fresh opportunity for manufactures to come in." He added "I'm really excited that engines are now going to be part of the equation and not just the spacer between the chassis and the gearbox. They're going to be an exciting bit that we can put back in and talk about and we can create relevance, again, for manufacturers and transport."

Fast forward six years and no new manufacturers have joined under the V6 regulations but they have fuelled the demise of Marussia and Caterham as their engine suppliers were their biggest single creditors. The former owed Ferrari $25.4m and the latter owed Renault $11.6m when they went bust over the past three years.

Brawn seems to have changed his tune about the V6 as he is no longer as "excited" about it. Yesterday he said that "despite being a miracle of modern engineering, it hasn't engaged the fans. It's low-revving, it's quiet, it doesn't stir the emotions in the way that we need to."

Changing the engine yet again appears to bring F1 into conflict with the view of FIA president Jean Todt who said earlier this year that "stability is essential - firstly, to have as much competition as possible, and then to protect the investment. You cannot invest in new technology every year, it is not financially sustainable, and we already complain about the cost of racing, the cost of Formula 1 - a cost that for me is absurd."

Todt added "I'm sure if you said, 'let's go back to engines from 10 years ago', many manufacturers would not support such a move. I'm convinced a minimum of three out of four would leave."

Let's hope he isn't right.