Robert Kubica volunteered to give up F1 testing time to help Williams

The Polish driver was originally due to run in the morning before handing over to Sergey Sirotkin to sign off Williams's pre-season preparations.

But with Stroll having lost valuable mileage over the two tests because of weather and car problems, Kubica approached the team on Thursday to suggest giving up his time for the Canadian.

Williams welcomed the idea and shuffled its programme around: running Sirotkin in the morning and Stroll in the afternoon.

Deputy team principal Claire Williams praised Kubica's attitude - well aware that he still harbours ambitions to grab a race seat in the future.

"It was actually under Robert's instigation," she said.

"Over the course of the seven days that we had here, the race drivers, through various different reasons, whether it be weather or directions that we've taken, haven't had the track time that we wanted them to ahead of Australia.

"As everyone knows, Robert is an incredibly considerate racing driver and we're very lucky in that and he knows that for the team's benefit, the race drivers need the maximum amount of mileage.

"So it was his generous offer yesterday. It wasn't the team.

"We haven't asked him. It wasn't Lance, Lance didn't ask him.

"It was Robert, it was off his own bat, and clearly we were going to accept that we need that our race drivers to be in a best possible position that they can be going to Australia.

"Having them both in the car today will help us."