Jenson Button claims he turned down a better offer from Brawn to take on the challenge of joining Lewis Hamilton at McLaren.

The 29-year-old, who wrapped up his maiden world title in Brazil last month, announced his move to McLaren on a "multi-year deal" on Wednesday, days after parting company with reigning constructors champions Brawn GP, who were the subject of a takeover by Mercedes-Benz earlier this week.

Button has explained his decision to terminate his long-term association with Brawn as the need for a new challenge after achieving his aims with his former team.

The Briton told BBC Radio Five Live: "I am actually earning less than I would have been at Brawn so it's not about the money and everybody involved knows that is not the case. It's because it's something new.

"I knew it would be a challenge to go up against Lewis in his environment and my goal since I was eight years old was to win the world championship and I've done that now and I feel in need something else, a new challenge."

Button admits his decision, which means the Woking-based company now have the last two world champions in an all-British star line-up, did not come easily.

"I was excited but there was a lot to think about because I'd been with Brawn for seven years," he added.

"On the emotional side there was definitely a lot to think about but I thought the challenge of going up against Lewis in his environment would be very tough but very exciting.

"I know the environment in both areas and I know what I want to do and I want new challenges."

Button also paid tribute to Brawn - "I couldn't have done it without him" - but accepted things will change from now on after he said goodbye to the Brawn mechanics.

"It's going to be a different relationship because I am not within the team any more, we're not fighting for a world championship together," Button added.

"We've achieved that goal so I am going to be a rival. We'll still have a good relationship, we've been through a lot together."

While he has not yet spoken to Hamilton, Button is certain the pair will be at the forefront of challenging for the title next year.

He said: "I think with both teams you can say there is a chance of defending your title with them: nobody really knows who is going to build the better car next season.

"History would say Ferrari and McLaren would build a very competitive car but last season Brawn came out with a stunner, a car that was beyond belief for a lot of teams so you never really know.

"You are always taking a gamble choosing any team but I do know there will be four or five teams at the front being competitive and I'm in one of those teams."