FIA technical delegate Charlie Whiting held a rare press conference for the assembled media in the Barcelona paddock this afternoon. The subject? The legality of the off-throttle blown diffuser currently being used by 75 percent of teams.

Earlier this week, it was reported that the FIA would ban teams from manipulating their exhaust gases to create added downforce while drivers were off the throttle, but Whiting has not yet prohibited the trick.

However, he did warn that teams using the off-throttle blown diffusers were putting themselves at risk of protest - and possible disqualification - should the other teams protest the device's legality. HRT, Virgin, and Williams are thought to be the three teams not currently taking advantage of the added downforce on offer.

While the concept of a blown diffuser has been around for years, teams have become more cunning in exploiting the gains. However, Whiting is concerned that recent progress in manipulating the exhaust gases while off the throttle has crossed the line into illegality.

"It became apparent to us through examination of data that what we thought was a fairly benign feature was turning into something that was being used, in our opinion, illegally," said Whiting. "An exhaust system is there for the purpose of exhausting gases from the engine, so when you are off throttle it is not doing that therefore driver movement is being used to influence the aerodynamic characteristics of the car.

"We were becoming increasingly concerned about the increase in extremes, shall we say. Then a bit of fuel, a bit of spark, retard, it was getting more and more extreme and that was the main reason for it.

"These things start off little and start off appearing to be quite benign," Whiting continued, "but then they get worse and worse and worse. And we are now faced with the possibility of even more extreme systems coming along, so we felt it was time to do something about it.

"Of course exhaust blowing is not new, it has been around for years, but I think Red Bull really took it to another plane with their low exhaust at the beginning of last year, and it became clearer and clearer through engine mapping that it was time to do something about it. It got more and more and more extreme. It is by no means unusual these things happen. It happened with brake ducts for example and aerodynamic appendages on brake ducts, and in the end you realise you have to do something about it."

While Whiting has not yet acted to ban the device, he warned the teams using it that a future ban was a real possibility if the others launched a formal protest.

A ban "is always a possibility," he said. "I've made that clear to the teams that it could happen and then we will take it to the stewards in the normal way. We have always maintained in all of our technical directives that we have sent for many years now that this is merely the opinion of the technical department, and anyone is free to challenge it in front of the stewards. It doesn't happen very often but it has happened in the past. As you know with the brakes in Brazil, for example, in 1998. But it can happen and I've told the teams that were pleased that we decided to postpone this introduction that it could happen."

At the senior team personnel press conference on Friday afternoon, Williams chairman Adam Parr gave his opinion on the legality of the blown diffuser.