Jake Humphrey, Paddy Lowe, Claire Williams, Lance Stroll, Sergey Sirotkin and Robert Kubica announced the 2018 F1 Williams car in London on Thursday. Picture: Steven Paston/PA via AP.

London - Williams Deputy Team Principal Claire Williams has defended the British team's decision to hand Russian rookie Sergey Sirotkin a seat for the 2018 season instead of a remarkable Formula One return for Robert Kubica.

Kubica will instead have to make do with a secondary role as reserve and development driver for Williams with Sirotkin, 22, partnering 19-year-old Canadian Lance Stroll as the youngest pair on the grid.

The Pole, who spent five years in Formula One between 2006 and 2010, has battled back to compete for a seat since a horrific rally crash in 2011 that partially severed his right arm.

Sirotkin's inclusion is believed to bring considerable sponsorship backing as the only Russian driver on the grid.

"Our decision making process is so much more complex than deciding to put a driver in a race car because they have some cash," said Williams (who will return to her duties this season after giving birth to her first child) at the FW41 car launch on Thursday.

"It's nothing new in Formula One that drivers come with money either and thank goodness that they do. I think it is incredibly naive to make the statement: 'he's just a pay driver'.

"It's great if a driver has financial partners, it's great for the team and the driver. It's an expensive sport."

However, Williams insisted driver safety remains the paramount concern and the team has no concerns about fielding such an inexperienced line-up.

"We would only put talented drivers in our car," she added.

"This a dangerous business and we are not going to put someone in our car just because they come with money."

Driver safety will be even more in the spotlight this season with the introduction of the halo head-protection device around the cockpit to protect drivers from flying debris.

And Williams' Chief Technical Officer, Paddy Lowe, believes complaints over how wishbone structures look will quickly be forgotten.

"The aesthetic has been a bit controversial but by the time of the second race no one will be talking about that," he said.

"Over the past 10 years there has been at least one incident per year where you have thought someone has been very lucky and it was only a matter of time before someone was very unlucky."

Agence France-Presse