Williams begin three-day Silverstone test.

Williams began their preparations for the Spanish and Monaco Grand's Prix today [Tuesday], by running two cars at Silverstone, Mark Webber working alongside third driver, Antonio Pizzonia.

The Grove based squad were going to be joined by Toyota, McLaren and Renault, however those teams have instead opted to go to Jerez, as poor weather is forecast in the UK. They are now scheduled to begin testing later this week on Thursday.

Despite the weather forecast though, Williams did complete some dry running this morning, before heavy rain engulfed the track this afternoon. Webber was quickest on a 1m 23.901, the Aussie managing 69 laps in total, while Pizzonia was around a second slower in the sister car. He completed 42 laps.

"The predicted wet weather front arrived slightly earlier than we thought it would this morning but we still managed to get a few hours of dry running," confirmed Williams test team manager, Tim Newton.

"This afternoon's session, however, was severely hampered by heavy rain showers. During the time we had on track, Mark and Antonio concentrated on wet tyre testing, set-up work and systems checks.

"The [weather] front seems to be moving fairly quickly though so we will hopefully be able to get a dry days' running tomorrow."

Nico Rosberg meanwhile will make his debut for the team tomorrow following the announcement that he has signed to be the team's second official test driver. The German will take over Pizzonia's FW27.