The row over blown diffusers suffered another shambolic twist today when the FIA did an about turn.

On Friday, shortly ahead of the opening practice session, Charlie Whiting ruled that for reliability reasons Renault engines - as used by Red Bull, Lotus Renault GP and Team Lotus - would be allowed to run at 50% throttle under braking. This followed a concession granted to Mercedes - whose engines power Mercedes (natch!), McLaren and Force India - whereby the German units were able to use an engine over-run under braking - like Renault for reliability reasons - in this case relating to crank case pressure.

However, following 24 hours of heated debate, referred to by Team Lotus boss Tony Fernandes as shambolic and not in the best interest of the sport or its fans, the FIA has this morning issued a directive (TD026) reverting to where the ruling stood on Thursday and thereby restricting Renault to just 10% throttle under braking.

"Following further discussions with teams and engine manufacturers we are now in a position to offer the following view which we will enforce with immediate effect," read the directive.

"In line with the requirements to provide acceptable SECU configurations to the FIA before the start of the British GP, ie before the start of the Event at 10am on Thursday, we consider any information provided after that time to be inadmissible for this Event.

"Therefore, for the reminder of this event the requirements of TD022-11 and TD025-11 stand as written and, an exception (of which every manufacturer was aware before the event) fired overrun will be permitted in FC04."

For much of this morning's practice session, Christian Horner and Adrian Newey, along with representatives from Renault and a couple of other teams, were in a meeting with the FIA in Race Control. Though Horner issued a firm "no comment" at the end of the meeting his anger and frustration was obvious. The Englishman has previously argued the 50% allowance is purely for reliability reasons not performance, and while Renault has been denied this its rivals at Mercedes have been given the all-clear.

Being an official directive there can be no further u-turns though Whiting could amend the regulations in time for the next Grand Prix (Germany).

While Sebastian Vettel went on to post the fastest time of the session, there are fears that this row will overshadow the event. Indeed, there is even talk of protesting the result.