Ross Brawn has admitted that Rubens Barrichello has a mountain to climb if he is to successfully catch and overtake Jenson Button for the 2009 F1 Drivers' World Championship - but he suggested only a fool would write off the 'hugely motivated' Brazilian's chances in the British Grand Prix this weekend.

Arriving at Silverstone, Button has amassed a commanding 26-point advantage over team-mate Barrichello in the chase for the coveted crown, courtesy of six victories from the opening seven outings of the campaign - equalling a record previously held only by legendary multiple world champion Michael Schumacher and the late Jim Clark - to none for the S?o Paulista, who indeed has mounted the rostrum on only three occasions so far this year, and has yet to get the better of the British star on race day.

Gearbox issues in the Turkish Grand Prix in Istanbul last time out conspired to ruin Barrichello's race from the start, and ultimately forced his first retirement of the season - prompting him to complain publicly afterwards that when things go wrong within the team, they always seem to do so on his side of the garage, as Button sprints on seemingly inexorably to title glory.

Indeed, the latter's margin over the first non-Brawn driver in the standings - Red Bull Racing's Sebastian Vettel - is a staggering 32 points, meaning he can afford to finish runner-up in each of the remaining ten grands prix and still lift the laurels at the end.

The Brackley-based outfit's team principal Brawn - usually a man to err on the side of caution and circumspection rather than optimism - has suggested that it will require a significant slice of bad luck now for the Frome-born ace to be toppled from his perch, though if Barrichello is going to fight back anywhere, he noted, Silverstone is probably his best shot.

"Rubens faces a massive challenge," the Englishman is quoted as having said by the Daily Mirror. "Jenson has been driving exceptionally well, and for Rubens to have a chance this year Jenson has got to start dropping points by not finishing or other problems. If Jenson continues driving the way he is, maybe he won't win races but he will still be there scoring strong points.

"Rubens is always extremely strong at Silverstone, though, because a lot of his early career was spent there. He seems to fit well with the track; he likes it and it suits his driving style. It's not a track that is sensitive to brakes, and that's often an area he finds quite critical on the car. I expect him to go very well this weekend. Jenson has won six races, but Rubens is still hugely motivated by the challenge of beating him."

Button, however, has sent out a warning shot that he will not easily be beaten in front of his adoring partisan supporters on home soil this weekend - and vowed not to lose his nerve, with compatriot Lewis Hamilton having rather uncharitably been labelled a 'choker' on occasion for snatching defeat from the jaws of victory when the stakes are at their highest.

The current world championship leader may never have ascended the podium in the British Grand Prix in nine previous appearances, but he is hot favourite to prevail around the Northants circuit on Sunday - and he has made no secret of the fact that should he do so, it would be the most memorable triumph of his career to-date.

"I've never felt myself choking under the pressure of having to perform at home," the 29-year-old insisted. "When you are driving you forget you are racing at Silverstone. It's not a home race when you put your helmet on - you're completely focused and it's just about winning.

"You enjoy it when you pass the chequered flag, but when you're racing you're very selfish. It's all about you and finishing first. That's the way you have to be as a driver."