The Mercedes and Red Bull bosses are both set to join Pirelli's Paul Hembery for a meeting with the FIA's Charlie Whiting in Suzuka today to discuss the testing venue.

The teams have split into two camps, with Mercedes leading the Bahrain side, and Red Bull the most vocal of those preferring to stay in Europe.

A third option, with parallel tests allowing teams choosing which one to support, has also become a real possibility.

As reported yesterday, testing outside Europe can only happen if the FIA and a majority of teams agree. To that end Niki Lauda composed a letter to the FIA, requesting permission for it to go ahead.

Lauda then personally canvassed teams, Ferrari, McLaren, Force India, Renault, Haas and Manor all signing along with Mercedes. A couple of those teams later told the FIA that they didn't necessarily want to go to Bahrain, but didn't mind if others did. Those who have not signed are Red Bull, Toro Rosso, Williams, and Sauber.

The majority of seven opens up the possibility of a test being held outside Europe, but there is a separate question over whether tests can be held in different venues.

Although it has always been understood that the teams must test together, the wording in the Sporting Regulations is ambiguous, and refers only to 'team tests'. Those now pushing for Bahrain, including Ferrari, have tried to demonstrate to the FIA that the rules don't specify a single venue.

Meanwhile, Horner is convinced that Mercedes has an ulterior motive in pushing for Bahrain, in that it wants to test its 2017 car and its cooling systems in hot conditions.

Pirelli asked Lauda

However, Lauda insists that in circulating the letter he was acting as a neutral party to help out Pirelli, and he is not working in a Mercedes capacity. The Austrian says he was personally asked to sort out the situation by Pirelli CEO Marco Tronchetti Provera.

Lauda told Motorsport.com: "Pirelli simply asked me, 'please you seem to be the only neutral, sensible guy here, we need a test in normal weather conditions. Which is only Bahrain.

"Why do we need it? Two weeks before the race it's the last test of tyres they are going to develop and guess out of the Abu Dhabi [mule car] tests in November, where afterwards completely different cars come, with 30 per cent more downforce.

"If you cannot test in Bahrain, two weeks before the first race we will not know what will happen. If we don't do this test properly, with a plus 10 degree celsius circuit temperature or whatever difference on Barcelona, then we have a problem in the first four races. This we don't want.

"Now, we have all this opposition from Red Bull and Mr Horner, which I do not understand any more. He says, 'I cannot test in Bahrain because the development of my new car goes to the last minute. If I go to Bahrain, I lose seven hours. That's the difference between flying a car to Barcelona, and seven hours more you have to fly to Bahrain. This is my serious reason.'

"Six signatures we need, I got seven. All I did was run up and down and ask, 'where do you want to test?' The best situation now, with all this political mess and everybody's ego running in all kinds of directions, is we have the possibility to have two tests. What the hell is going on here? You have Barcelona, at the same time Bahrain. Who wants to go to Barcelona, go to Barcelona, but why do the Barcelona testers hinder the Bahrain testers? I don't understand this."

Lauda is adamant that Mercedes is not pushing for Bahrain specifically because it has gone to the limits on cooling, and wants to test in hot conditions, as Horner suspects.

"We have a car which won the last two and half World Championships in a row, without temperature problems, so Mr Horner can be sure we know how much cooling we need wherever we go.

"So this is all bullshit. He wants to go Barcelona because it's easier for everybody and cheaper and better, why the hell go to Bahrain? We have to ask Pirelli, they are the only ones who need the test. We are testing for Pirelli a completely new tyre. Apart from that, we have completely new cars."

Red Bull not shown letter

Horner, meanwhile, claims that Lauda never even approached Red Bull with the letter, presumably because the Austrian already had the majority he required, and knew he would get a negative response.

Horner also expressed doubts that Lauda is acting in a neutral capacity just to help Pirelli – and suggested that pressure had been exerted to get some smaller teams to sign up.

"Niki has done a great job running around," Horner told Motorsport.com. "Unfortunately he forgot to show us the letter, which must be an oversight on Niki's part. I'm sure it was purely an oversight. I don't know whether Niki's got a holiday home in Bahrain or not, but he seems desperately keen to spend a couple of weeks out there!

"How often has Niki Lauda been neutral, as the executive chairman of Mercedes GP and particularly their engine department? As in 2014, they were always particularly keen to trial their cooling package. This is very little to do with tyres.

"We've got seven teams on the grid that are close to insolvency. Is it right to burden teams with those costs? And why have they signed? Privately, none of them want to go. But of course they have contractual agreements and commercial pressures upon them that are no doubt being used to persuade them otherwise."

Horner remains adamant that testing in Barcelona will be much more efficient than going to Bahrain.

"I think for me, we've got eight days of pre-season testing, it's a totally new concept of car, it's inevitable that things go wrong with a new car, when as far as I know all 11 teams are European-based, the costs and expense of being in Bahrain is anywhere between 500,000 and a million Euros of additional cost.

"If you have an issue at least if it's at Barcelona you can have a part on an Easyjet flight or even in the back of a van and 12 hours later it will be at the circuit. The logistical challenge of doing that in Bahrain the first time you are running the cars, for me it seems far too excessive.

"The difference in temperature with Barcelona is only on average seven degrees celsius at that time of year, and at Barcelona you have corners like Turn 3 and Turn 9 that will be flat and will put an enormous amount of stress into the tyre and give them a very good work out. I think the benefit of Bahrain is blown out of all proportion.

"For me this is a decision that should be made in the Strategy Group. We decided over a month ago that there were going to be two tests in Barcelona, everybody was happy with that, then subsequently there's been a big drive to test in Bahrain. Maybe a middle ground is one test in Barcelona, then one in Bahrain. But again the costs associated with that are horrendous."

Horner insisted that he had not told Lauda that RBR would lose seven hours of development time: "That's ridiculous. For a team like us, either test isn't a major problem. But at the end of the day I'm the guy signing off the expenditure, and I find it irresponsible to be wasting a huge amount of additional money for what could be done in Europe. It would seem to me illogical."

One major hurdle when it comes to split tests is that the FIA always attends the first tests because it has to trial its latest systems and ensure that they 'talk' to the new cars, while the official flat patch is available in the FIA garage for teams to check out their cars on the equipment that is used on race weekends.

The FIA cannot be in two places at once, so that automatically becomes a big compromise, as it cannot afford to wait until Melbourne to check that its systems work – although Lauda has suggested that the FIA simply spends one test at Barcelona, and the second in Bahrain.