Jenson Button proved he is fit to fight for the Formula One world championship by setting a personal best in the Mazda London Triathlon.

Now the British ace is urging his Brawn GP team to do their best to provide him with a car capable of taking him to the title.

Button, who uses triathlon training to keep in shape for the rigours of driving a racing car, crossed the line in the Docklands yesterday in an impressive 2hrs 7mins 2secs.

But the more important figure is his rapidly decreasing lead in the championship, which now stands at just 18.5 points with seven races to go.

After winning six of the season's opening seven Grands Prix, mainly in countries where the track temperatures have been hot, Button's Brawn GP car has not been as competitive on tyres that have lost grip in cooler Europe.

Button, whose triathlon exploits raised over £16,000 for the Make A Wish Foundation, said: "It's down to us to make the car work in those colder conditions.

"If we don't solve those issues, we're going to be gobbled up by the Red Bulls of Mark Webber and Sebastian Vettel which seem to be working in hot, cold, whatever."

The next Grand Prix is in Valencia on 23 August, and Button said: "We have to be out there challenging for wins, and that's exactly what we have to do immediately."

Britain's Will Clarke and Helen Jenkins won the elite races yesterday.