Rosberg ends Jerez test on top

The morning session was a total waste for the teams, however, as a thick fog only allowed them to start working almost at 1pm local time.

Before that, the circuit was covered in thick fog, which meant that helicopters were unable take off or land and so the drivers were not allowed to take to the track.

Once the fog cleared, both Honda and Williams got on with their programmes, with Rosberg emerging on top of the timesheets after completing a last-gap flying lap in the hybrid car powered with V8 engine. Rosberg's time was the quickest of the week.

The German driver finished over two tenths in front of Honda driver Barrichello, who also put on a last-minute strong performance to outpace teammate Jenson Button by 0.002 seconds in Honda's last test before they unveil their new car next week.

Both Button and Barrichello had a busy afternoon of work, completed over 220 laps between the two.

"Considering how little time we had we did very well," Button told autosport.com. "No reliability problems so we could run all afternoon. It is all about tyres. We went through a lot of comparisons. We have a big programme on tyres.

"In fact everyone is flat out on tyres but some people are not able to run because of engine or other things, so we had a very good day. This is the last test with this car so I cannot wait for the new one."

Williams test driver Alexander Wurz was slowest after only 28 laps, who like his teammate Rosberg had problems with the gearbox.

"It is quite normal to have teething problems when you have new car component, but I think we are on top of it now," Williams technical director Sam Michael told autosport.com.

"This is the last proper test with this car and after the launch on Friday we have a two-day exclusive test in Valencia where all three drivers will have a go in the new car and on Wednesday the second car will arrive"

Today's times:

Pos  Driver        Team                Tyres  Time     Laps
 1.   Rosberg       Williams-Cosworth    (B)  1:18.321   52
 2.   Barrichello   Honda                (M)  1:18.547  102
 3.   Button        Honda                (M)  1:18.549  120
 4.   Wurz          Williams-Cosworth    (B)  1:18.833   28

All Timing Unofficial