Lewis Hamilton will go all out in attack as he bids to win the final four races of the season, starting at Sunday's Singapore Grand Prix.

The defending champion has crashed out of the last two races on the calendar in Spa and Monza, in part due to his aggressive approach. But the 24-year-old said he had no intention of putting his attacking instinct on hold ahead of Sunday's race in Singapore, unlike a year ago where the then championship hopeful drove a conservative race to finish third.

"Last year, I was driving with one eye on the world championship and wasn't going to take too many risks," said the Briton, whose car this weekend will go through it's final upgrade of the season.

"I was happy to finish on the podium. This year, it's different. I know I'm out of the title hunt and I want to attack these last four races, pushing for all the wins as I can."

Countryman Jenson Button remains the firm favourite to win the world title with a 14-point advantage over team-mate Rubens Barrichello, despite the Brazilian having closed the gap with two wins in the last three races, and Hamilton believes it is now a straight title race between the Brawn GP pairing.

"They're unstoppable," said Hamilton. "Rubens has pulled out some serious speed out of somewhere and they are both going to apply the pressure to each other. The title is open to both of them."

Meanwhile, it has emerged that a member of the Renault team known only as 'Witness X' led to Flavio Briatore being banned from Formula One.

Evidence from the Crashgate inquiry released last night claims the witness came forward on the eve of the FIA World Motor Sport Council hearing to reveal the elaborate details of the plot.

According to Witness X, Briatore knew all about the plan to have Nelson Piquet crash deliberately and the architect was Pat Symonds, Renault's once highly respected director of engineering.

The FIA statement said: "Witness X was told of the idea suggested to Nelson Piquet Jr by Mr Symonds, whilst in the presence of Mr Briatore. Witness X objected to the idea. He did not know the plan was to be carried into effect until the crash happened."