Honda duo on top at Jerez

Barrichello was almost half a second quicker than his teammate Jenson Button, although their dominance of the times probably owed more to levels of fuel that everyone was running rather than a dramatic step forward in pace from the RA106.

Speaking to autosport.com, the Brazilian said: "We did a lot today. We did set-up work, electronic and some tyres for the future.

"But today was almost like the beginning of the season, when I was learning the car and really improving the set-up of the car in general. In particular we improved the braking stability, which is good."

Renault's Heikki Kovalainen was third quickest overall, as he worked on a tyre programme ahead of the German Grand Prix.

Teammate Jose Maria Lopez, who ended up 14th overall, was working on different set-up work that required much lower levels of downforce that are usually ideal for Jerez.

Kovalainen said: "We did more work on the tyres, mainly for Germany. We have found some which will be good and we even did some tyres for Istanbul. It is hard to judge any tyres on this track, but we have some data from last year so we should be okay. We did a lot today."

World champion Fernando Alonso has been drafted in for the final day of testing tomorrow to help work on tyres for the Hungarian Grand Prix.

BMW-Sauber's Robert Kubica spent the day focusing on tyres and set-up work, while teammate Nick Heidfeld once again evaluated a version of the sidepod wing that had been tried out for the first time on Wednesday.

Following earlier problems, a new wing - which had not been painted and was in pure carbon fibre black, was bolted onto the car.

"We did some aero work in the morning, and in the afternoon we worked on some tyres," Heidfeld told autosport.com. "It was kind of conclusive but we have to look  at data to decide the selection. As for the aero piece I am now quite sure we will use it in Germany."

Kimi Raikkonen was fifth fastest overall, while teammate de la Rosa completed engine work but only drove for half a day before suffering a problem.

His problem was not as terminal as Ricardo Zonta's though - who suffered a spectacular engine blow up on his first lap out of the pits at 9.15am. With fire damage to the car, the Brazilian was unable to get back out on the track, leaving all the day's work to Olivier Panis.

Other red flags during the day were caused by Kovalainen stopping on track in the morning, Heidfeld following suit two hours later, Barrichello late in the afternoon and Lopez spinning three times during the day.

Today's times:

Pos  Driver        Team                      Time      Laps
 1.  Barrichello   Honda                (M)  1:16.981   76
 2.  Button        Honda                (M)  1:17.403  102
 3.  Kovalainen    Renault              (M)  1:17.440  125
 4.  Kubica        BMW-Sauber           (M)  1:17.980   96
 5.  Raikkonen     McLaren-Mercedes     (M)  1:18.025   57
 6.  Heidfeld      BMW-Sauber           (M)  1:18.193   95
 7.  Coulthard     Red Bull-Ferrari     (M)  1:18.719   41
 8.  Panis         Toyota               (B)  1:18.802  127
 9.  Rosberg       Williams-Cosworth    (B)  1:18.996   63
10.  Doornbos      Red Bull-Ferrari     (M)  1:19.104   48
11.  de la Rosa    McLaren-Mercedes     (M)  1:19.134   36
12.  Liuzzi        Toro Rosso-Cosworth  (M)  1:19.216   65
13.  Monteiro      MF1-Toyota           (B)  1:19.286   75
14.  Lopez         Renault              (M)  1:20.634   47
15.  Zonta         Toyota               (B)  No time     1

All Timing Unofficial