World champion Lewis Hamilton has expressed his surprise at Ron Dennis's decision to sever all ties with Formula One.

Dennis mentored Hamilton from his karting days through to becoming the 2008 world champion, but after taking a back seat earlier this year, the 61-year-old yesterday stepped down from his role as chief executive of McLaren Racing.

It was a disappointing end to his 28-year reign at McLaren with the team struggling to compete this season whilst also being embroiled in controversy after they were found guilty of misleading stewards at the season-opening Australian Grand Prix.

McLaren have been called before the FIA's World Motor Sport Council on April 29 to answer charges of bringing Formula One into disrepute for that incident, and Hamilton admitted he was surprised that Dennis chose to step down when he did.

"I wasn't disappointed, I was surprised," said the 24-year-old. "I hadn't heard about it, I was just as surprised as the rest of the team.

"Ron has been a huge force and support in my life and still plays a key role in my life.

"You guys have been writing about it for years - as soon as he gets to a certain stage he was going to move aside and he decided to do it now."

After the FIA's International Court of Appeal ruled the controversial 'double-decker' diffuser legal on Wednesday, McLaren were quick to try a revised component on Hamilton's car in practice today.

The defending champion showed something like his past form by going on to top the timesheets in first practice ahead of Brawn GP's Jenson Button.

Hamilton's future at McLaren has been subjected to scrutiny since Melbourne but the Stevenage man insisted he was happy at the team, although he stopped short of making a firm commitment for the future.

"I'm contracted to the team and I'm happy where I am," he added.