Following Pitpass' exclusive news earlier today that 17 F1 circuits have unified to oppose the 12,000rpm engine due to be introduced in 2014, technical figures met in the Valencia paddock and agreed to increase the limit to 15,000rpm.

The 17 circuits, including Monaco, Monza, Spa and Silverstone, are threatening to leave F1 and join IndyCar if the engine power doesn't stay at its current 18,000rpm. Their representative Ron Walker confirmed to Pitpass' business editor Christian Sylt on Sunday evening that despite the teams' latest concession, the threat still stands and he reiterated that it is far from idle.

"They will never get away with it. It must be 18,000 revs and it must sound the same," says Walker adding "that is what we agreed and if they don't do it then there will be promoters pulling out. The teams have got no regard for the customers, it is all about them."

Although the meeting in Valencia was not a formal gathering of the Technical Working Group, it is understood a letter was sent by the teams to the FIA's Charlie Whiting expressing their support for the plan to set the revs at 15,000rpm. This is now expected to be put tomorrow to a fax vote of the FIA's World Motor Sport Council which has until 30 June to redefine the technical regulations. If they stay as they are, with 15,000rpm engines, Walker says it will spell the end of many classic F1 races.

"If the teams want to have a brawl over this they are going to get the biggest brawl of their life. They won't be able to introduce the engine because we won't run the engine. We won't run the races," he says adding "an IndyCar race costs about three and a half million compared to what we are paying and it is louder and noisy. If the teams want us to go that's fine. If they don't comply with the letter I wrote, which was agreed, then hell will break loose."

It looks like the 15,000rpm engine will indeed be introduced as one paddock source confirmed to Pitpass "I gather that a 15,000rpm rev limit will be adopted, and that it won't negatively impact the environmental credentials of the new engine."

Paddock speculation has suggested that Walker's comments were prompted by F1's boss Bernie Ecclestone and not the fact that 17 of the sport's circuits have given Walker their approval to oppose the new engines. The source adds that "I also gather that Ron Walker was encouraged to say what he said by Bernie Ecclestone. Certainly, no-one in the paddock is taking what he said even remotely seriously." This could well be their undoing.

Even if the comments, and the circuits' decision, was prompted by Ecclestone (and Pitpass has no evidence that it was) it seems unreasonable to suggest that it shouldn't therefore be treated seriously since Ecclestone is of course the boss of the sport and controls pretty much all aspects of it. Regardless, Walker stresses that this is not at all the case and he told Sylt "I can assure you that Bernie didn't put me up to anything. I'm my own man. He came along to our meeting as a guest and listened to what we had to say and even our friend from Ferrari came in and listened to what we had to say."

As Pitpass reported earlier today the circuits' decision to unify is one of the most significant business moves in the history of F1 and could affect everything from the engines to any future sale of the sport.

Regardless of whether or not the circuits need to leave F1 due to the engines, their unification will stay and Walker repeats that this is "the first time that the promoters have ever got together and opposed in 50 years."

F1's day of reckoning is coming tomorrow whether teams realise it or not.