The FIA appears to have approved an exhaust design being run by both Williams and Caterham, which others teams have suggested is not legal.

Speaking at Jerez, where Williams was running its 2012 car but Caterham was running its 2013 contender, Lotus Technical Director James Allison voiced what many along the pitlane had been thinking since the green and yellow car had been unveiled.

"There is one feature of the Caterham's exhaust that I don't think will be there when we get to Melbourne," he said. Specifically his concerns seem to relate to a small deflector in the channel where the exhaust exits.

At the end of 2011, as a direct response to the blown diffusers many teams had developed, the FIA amended the regulations surrounding exhausts and how teams were allowed to use the expelled engine gases. The Caterham solution - and a similar design used by Williams - appeared to be in breach of those regulations.

Caterham was dismissive of the intrigue and when asked by Pitpass if the team had been in contact with the FIA over the design a spokesperson simply stated that the team is "evaluating a number of items as part of our pre-season test programme."

Shortly after this morning's unveiling of its FW35, Williams was the subject of similar speculation however, the Grove outfit claimed it had the approval of the FIA.

"The team spoke with the FIA this morning which is when they gave us their view," said a spokeswoman. "The team are now seeking further clarification on this and a decision as to whether this design will be carried forward will be made before the first race."

However, while it is a case of (almost) anything goes during pre-season testing, things can, and probably will, change dramatically if there is still a question mark of the exhaust design when the teams arrive in Melbourne for the season opener on March 17.

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