Martin Whitmarsh and Christian Horner clashed at today's official press conference in the wake of further changes to the blown diffuser rules.

Earlier this morning, the FIA revised the rule regarding how much exhaust flow Renault could still use when a driver is off throttle following claims that the initial 10% granted would lead to reliability problems. Consequently, it issued a new directive allowing Renault, which supplies Red Bull, Lotus Renault GP and Team Lotus to use 50%.

However, concessions had also been made to Mercedes, which, other than its own team, supplies McLaren and Force India. In the case of the German manufacturer, it was allowed to keep firing half its cylinders as engine over run in an attempt to ease pressure on the crank case.

Basically, the engines supplied by Renault and Mercedes, indeed all four current manufacturers, work differently thereby making it impossible for the FIA to come up with a 'one size fits all' directive.

At this afternoon's press conference however, Whitmarsh and Horner clashed, leading to Lotus boss Tony Fernandes describing the whole episode as shambolic.

"First of all there was a technical directive which effectively turned it all off," said Horner. "That was obviously met with reticence by the manufacturers and it has been very much a manufacture issue.

"Certain teams were then allowed to have fired overrun, to fuel their overrun, of which there are also, obviously, secondary benefits through the exhaust plumes and thrusts that that creates but that was permitted," he continued. "Obviously Renault presented their position to the FIA, and let's not forget that this is an extraordinarily complex matter, to demonstrate that precedent is there that, for purposes of throttle blip and reliability, that cold air blowing open throttle was a necessary part of the operation of their engine, otherwise it would cause serious issues. It would be unfair to allow fire overrun and not allow the same parameters for another engine manufacturer.

"I think it's a very, very difficult job for the FIA to pick their way through this and I think all credit to them, they've looked to try and be as fair, balanced and equitable as they decreed that they would be through the technical directive, to come up with the solutions that they have. We're not totally happy with the solution that we have, that's for sure. I'm sure Martin isn't with his and I'm sure there are a lot of conspiracies in the paddock that these are the reasons why Red Bull is performing or McLaren is performing, or some cars aren't performing. That's just circumstantial at the end of the day. The fundamentals are that the engine manufacturers have been treated in a fair and equitable manner."

"I'm sure people set out to do that," replied Whitmarsh. "I think there have been about six technical directives on the subject so far and it's moved around and when the goalposts are moving partway through a practice session, then I think it makes it quite difficult.