The championship leaders arrived at Silverstone with a raft of upgrades as the teams’ race to out-develop each other reaches a critical stage.
McLaren had been quick in the first session, but Lewis Hamilton could only manage eighth quickest in the afternoon, while team mate Jenson Button was half a second behind in thirteenth.
Last night, mechanics were wheeling away parts from the car as they abandoned any hope of running with the new package after it continued to handle badly.
McLaren are not the only team having issues with trying to copy Red BullÃ¢â‚¬â„¢s blown diffuser. In Valencia, Mercedes unveiled their version which went on to melt the bodywork.
Red Bull accused McLaren of sandbagging as their rivals know little about their real pace at Silverstone ahead of SaturdayÃ¢â‚¬â„¢s final practice, but the way the McLaren handled on Friday showed anything but that as Hamilton was 1.5 seconds slower than Webber, and Button two seconds slower.
The talk in the paddock is that McLarenÃ¢â‚¬â„¢s best hope of a good weekend now is a wet race. It might have been a scorcher for the last couple days, but there is rain in Scotland and the north of England, and the teams, as ever, are monitoring the situation.
It is worth remembering that the McLarens finished second and third behind Vettel in Valencia, and prior to that completed a one-two at the previous races in Istanbul and MontrÃƒÂ©al.
Hamilton has already won at Silverstone, so has tasted home glory. Button on the other hand has not, but recognises the bigger picture can be more important in terms of the championship.
If McLaren can still finish in the top six and keep the points deficit to Red Bull low, they will still be leading the driversÃ¢â‚¬â„¢ and constructorsÃ¢â‚¬â„¢ championships going to the German Grand Prix at Hockenheim.
There is still the rivalry between the two McLaren drivers, and it will be interesting to see how that plays out as they battle to show the Silverstone crowd who is the dominant British driver.
We all remember the now infamous clash between Webber and Vettel at the Turkish Grand Prix, and the wheel-to-wheel racing from the McLaren pair later in the race. Team principal Martin Whitmarsh will surely remind his drivers to keep their head in the pre-race briefing.
All drivers talk fondly about the tradition and history of Silverstone and for many teams it is their home race in front of the British fansÃ¢â‚¬â€it will always be a special occasion.
FerrariÃ¢â‚¬â„¢s Fernando Alonso has to be the most dangerous rival for Red Bull on Sunday, while MercedesÃ¢â‚¬â„¢ Nico Rosberg has been sniffing about the top four. McLaren, however, could surprise us on Saturday afternoon, as they very often do.
MORE: The latest football news
MORE: The latest tennis news