Picture: Graham Hughes/The Canadian Press via AP.

London - The Williams Formula One team has extended its engine partnership with Mercedes to the end of the 2025 season, the team announced on Friday.

Former champion Williams, which has not won a race since 2012 and which is currently last in the championship, has used Mercedes power units since 2014.

The existing deal ran until the end of 2020, after which the sport is set for a major overhaul with revised technical rules aimed at producing closer racing and a budget cap introduced to level the playing field among teams.

"We believe that they (Mercedes) will continue to have an extremely competitive engine package," said deputy principal Claire Williams, whose team finished third overall in 2014 and 2015.

Williams will continue to provide its own transmission, unlike Racing Point which is supplied with both engine and gearbox by Mercedes.

Mercedes' own factory team has won every championship since the 1.6 litre V6 turbo hybrid engines were introduced in 2014. The team is heading for its sixth successive driver and constructor titles this season.

The extended partnership can be read as a vote of confidence in Formula One's future with Mercedes, which is making its debut in the all-electric Formula E series from November, committed at least as an engine provider after 2020.

Formula One's current commercial agreements with the teams expire at the end of next year.

Mercedes motorsport head Toto Wolff recognised that Williams, struggling with an uncompetitive car and only one point scored in 14 races this year, was going through tough times.

"That has only served to demonstrate their resilience and strength of character as they battle back to where they belong on the grid," said the Austrian, who was previously a shareholder in Williams.

"I am certain that the outlook for independent teams is bright under the financial regulations that will be introduced from 2021 and we are delighted to continue our partnership with Williams into that new era of our sport."

Williams has Mercedes-backed rookie George Russell, last year's Formula Two champion, in its driver line-up along with Poland's Robert Kubica.

Russell, 21, is seen as a future Mercedes driver but is set to stay at Williams in 2020. 

Reuters