Williams' inability to be ready for the start of testing ahead of the 2019 Formula One season has been branded "embarrassing" by deputy team principal Claire Williams.

While nine teams rolled out onto the Barcelona track on Monday and Tuesday, Williams were notable by their absence, their FW42 car not ready to begin collecting data.

That left George Russell and Robert Kubica sat twiddling their thumbs as the rest of the paddock put the miles in at the Circuit de Catalunya.

The British team were finally able to get their season underway on Wednesday, but it could not ease the frustration felt by Williams.

"It became apparent quite late on that we weren't going to firstly make the shakedown and then subsequent to that, not make the first day," she told reporters.

"We thought we could get everything that we needed together in order to make Tuesday, and then parts just weren't coming through as we hoped they would, and in the time that we hoped that they would.

"So, it transpires that we didn't make it until today. But I am not going to go into any detail as to why that happened. I don't think that it's appropriate to discuss the ins and outs of what went wrong. Completing that inquest anyway has not happened at Grove yet.

"We're clearly aware of some of the issues, but it's too early in the day to start discussing them in any detail and probably something that we wouldn't do anyway. We need to resolve what went wrong or analyse what went wrong, and then to resolve it so that this doesn't happen again at Williams."

She continued: "We can only apologise. I would apologise to our fans, I would apologise to all the people that have had the pressure really dialled up on them at Grove over the past few days to get everything ready, just to get us to this point today, and mostly to George and Robert, who were looking forward to a car on Monday so that they could prepare and have the most amount of time possible to prepare ahead of the season.

"But they have been fantastic in this, they have been very understanding and very supportive."