Jenson Button says that he is performing as well as he is in 2010 because he has nothing left to prove - either to himself or the critics that followed his first ten years in Formula One.

Speaking after free practice for the Spanish Grand Prix in Barcelona, the McLaren driver insisted that having won the 2009 world championship had lifted a weight from his shoulders and, even after opting - against paddock wisdom - to join Lewis Hamilton at McLaren, is allowing him to enjoy his racing more than ever.

Button has won two of the four races held so far in 2010, in changeable conditions in Australia and China, and currently sits atop the world championship standings, with team-mate Hamilton fourth and twelve points adrift. Although not quite as dominant as he had been heading to Spain last season, the 30-year old has used his experience to succeed where others, notably Hamilton and the pacesetting Red Bulls, have failed and it is clear that he is enjoying life at the top of the F1 tree.

"I've won the world championship, I've achieved my goal that I set out to achieve," Button told Reuters, "If my career ended now, I would end my career as a very happy person. I've got some great stories to tell and I can look at my trophy on the mantelpiece and say 'I've won the world championship in F1 - how many people did that?'."

Having unveiled a plaque dedicated to his title on the Circuit Catalunya's Avenue of Champions between practice sessions on Friday, Button admitted that, even though he had achieved his goal of becoming number one, the fire still burned to do it again.

"I'm here and I want to achieve more this season - I want to win the championship," he insisted, "I've achieved what I set out to do, so I have no pressure. I'm not putting pressure on myself, and I'm so much more relaxed as a person and as a driver.

"It means I've more time to think, and more time to try and make myself a better person and a better driver, so I couldn't possibly be in a better position at the moment. I know how I feel inside, and I'm the best person to judge myself. I'm very critical of the way I am, the way I drive, how I act within the team and also as a person."

After losing time in the pits to investigate possible damage to his McLaren, Button ended the opening practice session in Barcelona second only to team-mate Hamilton, before the afternoon session saw the pair slip slightly down the order, ending the day in fifth and ninth.