Jenson Button topped the timesheets at the Circuit de Catalunya today, posting the fastest time of the week thus far.

While some remain sceptical of the Brawn's pace, Flavio Briatore notably telling Gazzetta dello Sport, "If you have no sponsors for your car, you come here to make big lap times", others believe the Brackley team could produce some real surprises this season.

Button completed a full race distance complete with pit stops in the morning, followed by a qualifying simulation and various set-up evaluations in the afternoon. It was another highly successful day for the team and saw the Englishman complete an encouraging 130 laps. Rubens Barrichello will take over tomorrow to conclude the team's first test.

"It's been another great day and a very positive test generally," said Button. "It's so good to have achieved a full day's running, including a race distance, without any issues and it's fantastic that we clocked up so much mileage. After the challenges we have faced, to come here and get off to such an encouraging start is just what we all needed and I can't thank the team enough. All that effort has really paid off and everyone can feel very proud."

The day got off to a bad start for Felipe Massa, who took over from Kimi Raikkonen. The Brazilian went out on track just after 09:00, but had to stop by the side of the tack due to a hydraulic problem. The necessary repair work took over two hours and it was 12:10 before he was able to begin a race weekend simulation. Unfortunately the first part, the qualifying session, was not concluded because there wasn't enough time left after another car stopped on track.

The rest of the day went well for the Italian team however. After the lunch break Massa started the race simulation and completed it successfully, in contrast to Kimi Raikkonen's attempt yesterday. The Brazilian completed 109 laps, finishing 1.041s off the pace of what the Maranello outfit described as "the surprisingly fast Brawn GP of Jenson Button".

For BMW, Robert Kubica concentrated on several different race-related situations in order to fine tune the working relationship between him and his pit crew. He also worked on solutions for the set-up of the F1.09 on the mechanical and aero side of the car. As well as this, he tested different tyre options and, before the lunch break and after the end of the afternoon session, did a couple of practice starts.

"Today was very productive", said the Pole. "We tried various solutions we weren't able to complete last week in Jerez because of the unfortunate weather conditions. Obviously our main target today was to do a lot of evaluations for the forthcoming Australian Grand Prix."

Toyota had another busy day with Timo Glock taking over from Jarno Trulli. The German ran through a programme of aerodynamic evaluations, suspension and set-up, clocking up 132 laps despite some interruptions for red flags. He will return to the cockpit tomorrow for Toyota's last day of winter testing for the 2009 season.

"This morning started well," said Glock, "we made it through a lot of set-up and comparisons in the course of the day. We found some different directions and overall it was a productive session. Late on we had a slightly longer break so we couldn't quite finish our plan. But we should have enough data to investigate and make some positive steps for tomorrow."