The information was revealed by autosport.com – the online edition of the Autosport magazine – after a source within the FIA confirmed the talks between the international body and Toyota on the matter. The source also told the aforementioned site that the FIA has already approved one of the different designs, only it didn't mention which one: Toyota's or Williams'.
“The FIA has had some correspondence with Toyota about diffusers but hasn't actually seen what they've been testing. One design has been approved by the FIA but we cannot confirm that it is the design in question,” said the source.
FIA's approval of one of the two rear diffuser designs may lead to major aerodynamic revamping – of the rear section – from most teams within the F1 paddock. As reported by Autosport magazine the other day, Toyota's system is based “in a 15 centimetre wide zone at the centre of the car where teams are allowed to fit extra bodywork”, while Williams' has “a low centre section, well below the 175mm height limit”.
However, until the FIA doesn't give the two teams a clear answer on the matter, both designs are very much illegal. Considering the FIA has only conducted talks with Toyota with a clear reference to the rear diffusers may lead us to thinking that the Japanese manufacturer made the better call. The FIA are expected to officially clear the matter in the next few days, ahead of the Bahrain testing in early-to-mid February.