**Formula One world champion Jenson Button said the prospect of going head-to-head with former champion Lewis Hamilton was what lured him to McLaren.**Button left the Brawn team, now owned by Mercedes, to join the 2008 champion Hamilton at McLaren earlier this week.
“I thought the challenge of going up against Lewis in his environment would be exciting,” he told BBC Radio 5 live.
“I’m earning less than I would have at Brawn, so it’s not for money - everyone involved knows that’s the case.”
Button spent five years with his former team, racing under the names of British American Racing, Honda and Brawn, before winning his first world title at the age of 29.
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Brawn only came into being a year ago when Honda pulled out, and had a miraculous debut season, winning the constructors’ title as well as powering Button to success.
And he admitted it would have been hard to recapture the thrill of his first season at Brawn if he had stayed.
“Not many people are ever in that position that I found myself in,” he said.
"At the end of 2008 I was excited about 2009 with Honda but that ended on 5 December and I was lost - I didn’t know where I’d be racing.
"When I jumped into the Brawn in March and realised we had a monster, it was a special feeling for the whole team after what we’d been through - I’m not sure if that emotion will ever be there again.
"My goal for 21 yeas was to be world champion - I’ve done that, so I need a new challenge which is why I did it.
"I had a good relationship with Brawn, especially with (team principal) Ross Brawn himself, who helped me to the championship.
"It was a real team effort and the normal progression for someone who is champion is to stay.
"But for me this is exciting, and that is what I need right now.
"I’m not sure if it’s the same for everyone but I always want a new challenge and I’m very excited about it.
“I know I’ll have to work hard to achieve what I want in 2010.”
The pairing of Button and Hamilton at McLaren makes them the first team to have two British world champions since Graham Hill and Jim Clark were together at Lotus in 1968.
Brawn have now been renamed Mercedes Grand Prix and have already signed German Nico Rosberg as one of their drivers.
His compatriot Nick Heidfeld is the favourite for the second seat.*