Jenson Button has likened his championship position to being the wearer of the yellow jersey with tired legs at the foot of a mountain climb.

Jenson Button has likened his championship position to being the wearer of the yellow jersey with tired legs at the foot of a mountain climb.

The Brawn racer is 18.5 points ahead of Red Bull's Mark Webber in the drivers' standings, but three difficult races ago he was far ahead and reportedly to cruise to the 2009 crown.

Button, 29, begins his summer break this weekend by contesting the London Triathlon.

"We've got to sort it out. We're leading the championship, but it is inevitable they are going to overtake us if performances keep going like they are," he said.

Three full weekends will pass before the F1 circus heads to Valencia, with factory closures to save money for teams throughout the August summer break.

"If we can't get a good result in Valencia we're screwed," Button added.

"It's like wearing the yellow jersey knowing that when you get to the mountains you're going to be useless and overtaken."

Sebastian Vettel had an even worse weekend in Hungary, starting from second on the grid but clipping Kimi Raikkonen at the start and later retiring with car damage.

The German has fallen 4.5 points behind teammate Webber, while his deficit to leader Button increased to 23.

Asked by the news agency SID if his title hopes can now be written off, Vettel answered: "No, there are still many races to go, and we have seen how quickly the tide turns.

"But it's no big secret that we know we can't afford anything else like this," the 22-year-old added.