Two British motorsport stars, each battling for a 2009 world championship, will go up against each other in the Mazda London Triathlon on August 2nd.

F1 title leader Jenson Button initially threw down a challenge to fellow F1 driver Lewis Hamilton, but the McLaren driver backed out and has now been replaced by Bradley Smith.

18-year-old Smith is currently third in the 2009 125cc World Championship, having scored two wins, three podiums and one pole position so far this season.

Smith challenged Button after they met at Silverstone during the British F1 Grand Prix where Smith, in recognition of his achievement of being the first British rider in three decades to lead any Motorcycle Grand Prix World Championship, was attending as a guest of Bernie Ecclestone.

Button's father, John, is a keen follower of MotoGP and began talking with Smith, leading to the meeting between the two racers. Their combined loves of motorsport, triathlons and competition came to the fore and Smith, eager to fill the gap left by Hamilton, challenged Button to a race in the Mazda London Triathlon, the world's largest triathlon.

Despite his young age, Smith is no newcomer to triathlons - the swimming, cycling and running events are a major focus of his training regime and his personal trainer is an ironman regular who has been passing on all his experience to Smith.

Button however, is the bookies favourite; the 29 year old regularly competes in triathlon events and, like Smith, also uses the three disciplines as a part of his fitness programme.

"When I met Jenson I told him straight away that 'Lewis won't race you but I will!'," confirmed Smith. "I've made sure I'm in the same wave start time as Jenson so we really get to battle head to head. Jenson has been really good about it and we've been swapping the odd text in the build-up to the race.

"Hopefully at the end of this season we will both win our respective championships which is fantastic for British motorsport but there's only going to be one winner in the triathlon and I'm planning on making sure that it's me!" he declared.

Button is using the triathlon to raise money for Make A Wish Foundation UK, while Smith will be supporting the Riders for Health charity.

The two motorsport heroes will be amongst 13,000 competitors raising a combined total in excess of ?3 million for charity.