The brief controversy about the design innovation that proved one of the key components of Brawn's 2009 title campaign had long passed into F1 history for many.

But more recently, repeated references to it have emerged once again, with Red Bull boss Christian Horner and design chief Adrian Newey both making unprompted remarks about it in recent weeks.

Horner said: "We have a situation in the sport, and forget Red Bull a little bit, but like the double diffuser was a battle between FOTA and FOM, that the engine is a very powerful tool for who has control of F1."

While Newey suggested the 2009 issue involved politics between then FIA president Max Mosley and leading teams McLaren and Ferrari.

"It was down to the fact that Max Mosley at that time wanted to teach a lesson to Ferrari and McLaren," he claimed.

Here we look at the background to the issues and why the 2009 affair has relevance to today.

The double diffuser affair

Over the winter of 2008/2009, three teams – Brawn, Toyota and Williams – exploited a loophole in new aerodynamic regulations to create the 'double diffuser'.

The design helped deliver added downforce at a time when new aerodynamic rules had been introduced to cut it back by around 50 percent.

The diffusers had become a big talking point in pre-season testing, but all three outfits were confident that they were not doing anything illegal.

That was because, as part of a new rules process originally introduced years previously by Mosley, they had sought the opinion of Charlie Whiting as to whether, in his opinion, they were legal.

As Mosley explained in his 'Formula One and Beyond' autobiography last year about the process: "Early in my presidency, we invited the teams to start submitting their latest ideas in strict confidence at the design stage.

"Charlie would look at the design and offer an opinion as to its legality. This was on the clear understanding that he was only giving an opinion, not a ruling, but nevertheless an indication of the line the FIA technical department would take."

He added: "Sometimes he would discuss a borderline idea with me. I never ceased to be fascinated by the ingenuity and originality of some of the concepts."

Whiting duly proffered his opinion that the double diffuser was okay, but that did not prevent rivals being free to protest it to race stewards if they wished so.

Indeed, at the Australian Grand Prix, Ferrari, Renault and Red Bull all protested the designs, with BMW Sauber following suit in Malaysia.

Their claims were thrown out by the stewards and in the end the matter went all the way to the FIA's Independent Court of Appeal, which after much controversy deemed the designs did comply with the rules.

Brawn, Toyota and Williams' rivals all had to follow suit and copy the innovation.

Why an issue now though?

It may seem hard to link current affairs to the double diffuser matter, but there are clear links between what is going on in F1 currently and what was going on in the background then.

On the one hand, Red Bull's references may well be fuelled by it reflecting more on the foundations of its title successes between 2010 and 2013.

For Newey admitted that Red Bull's mistake in not pursuing the double diffuser in 2009 proved costly to its title ambitions, and fuelled the foundations for it pushing everything to the limit going forward.

But there are also some political similarities too.

Like now – where manufacturers Mercedes and Ferrari are up against Bernie Ecclestone and FIA president Jean Todt – there was a battle for control of the sport back in 2009.

Mosley had come off the back of the 2007 'spygate' controversy and was motivated by the need to save costs against the push back from manufacturers, which had got together to form the Formula One Teams' Association.

But whereas the landscape in 2009 revolved around costs and the threats of a breakaway, the situation now involves power units and the need to stop F1 collapsing.

F1's manufacturers have been requested to come up with solutions to sort out the sport's engine crisis by January 15, otherwise Todt and Ecclestone may opt to act on a mandate they have been given by the FIA to look into changes to the sport's governance processes and rules.

If they are not happy, the option of an independent engine for 2017 – which Red Bull are so eager to want – could become real.

The battleground over the next few weeks will be of how the agendas of Todt, Ecclestone and the top teams line up, with engine rules central to the fight just as teams felt the double diffuser issue was in 2009.

But while Todt and Ecclestone are clear that they want to stop control of F1 being seized by two car makers, is it correct to say that Mosley had his own hidden agendas last time around?

Mosley influence

Had the double diffuser issue been purely a Mosley vendetta, it would have meant that he would have had to have direct control over Whiting, race stewards in Australia and Malaysia and all the judges at the Court of Appeal.

Accusations that Mosley has influenced such judicial processes are nothing new, but the former FIA president has always insisted that the right checks and balances were set up to ensure that could not happen.

In fact, in a letter he sent to the FIA WMSC amid FOTA's breakaway saga in 2009, Mosley said he had actually pushed back against calls from one manufacturer to have a say in the outcome of the double diffuser affair.

In the letter, he said: "We have heard a lot from FOTA about an independent court of appeal. Yet during the controversy over the "double diffuser", a manufacturer team repeatedly lobbied me (wholly improperly) to intervene with the FIA Court of Appeal and have the double diffuser declared illegal.

"The FIA Court would never listen to such an approach but it shows that for the team in question, 'independent' means independent of the other teams and under the control of particular interests."

Independence

Mosley has long made clear that one of his big annoyances was that he was regularly accused of having an influence over the judicial processes of the FIA.

In his autobiography Mosley explained about the International Court of Appeal: "The judges were all elected by the FIA member organisations and were the sort of people who would have been outraged had I, or anyone from the administration, contacted them – directly or indirectly – to suggest what they should decide.

"Anyone with knowledge of the UK Bar, for example, would have known that the idea of me calling up either of the two British judges...to suggest what they should decide would be nothing short of absurd. Given all that effort, it was disappointing that anyone should think the court was not fully independent."

Those words ring true today.

Mosley response

Mosley has kept a close eye on current events in F1 – having joined Ecclestone at the end of last year for a video interview discussing the future of the sport – so is well placed to comment on potential similarities between the double diffuser affair and what is going on now.

He is adamant on one thing: that there was no motivation in using the diffuser affair for political gain.

Ahead of the pending January 15 deadline for manufacturer engine proposals he also offers us a typically timely view.

"The truth of the matter is I was unaware of the double diffuser until Ferrari started complaining and Brawn, Williams and Toyota had built their cars," he said this week.

"I watched the protests with interest but there was never any question of intervening. Adrian Newey's suggestion that I used it as some sort of weapon against Ferrari and McLaren is quite simply wrong. He should have read my book!

"In fact, had the FIA been prepared to act illegitimately, we could have destroyed FOTA early in 2009 by banning the double diffuser in return for Ferrari abandoning the other teams, the exact opposite of Adrian's theory."

Mosley also has an interesting take on what way forward F1 should be taking ahead of January 15.

"The current problem revolves round engine costs and supply," he explained. "The solution would be rules allowing only two engines per car per season.

"This would simultaneously double supply and halve costs. Today's engines would require only a modest adjustment to achieve that.

"The engine suppliers would immediately say it was impossible and would be a disaster, but in the history of F1 there has never once been a case where such predictions have proved accurate".