Symonds admits Williams "let down" by 2016 developments

The Grove-based team finished third in the constructors' championship both in 2014 and 2015, but has been unable to match those performances this year.

Williams is currently fifth in the standings, 10 points behind Force India, with four races remaining.

Symonds conceded the team has been "remarkably stagnant" this season, and says the upgrades introduced throughout the season have not performed as expected.

He also acknowledged Force India's progress has been "exceptional".

"I think we've been remarkably stagnant this year. I think other teams, particularly Force India, have moved on," said Symonds.

"Force India did most of it in one upgrade, which is quite unusual these days because you tend to trickle things race by race.

"At Barcelona they made a pretty major step forward and while it may not have been quite as apparent in Barcelona, I think it took them a little bit of time to understand how to utilise it. On the other hand, we have produced upgrades, we have improved the car.

"There's no doubt that if we went back to Barcelona now we'd be a bit quicker, but the delta wouldn't be as much as Force India. They have done an exceptional job.

"And I think our development, which has been pretty strong from 2014, particularly in 2015, has let us down."

Although Williams made an early switch to focus on the development of its 2017 car, Symonds says that is not an excuse for the team's form this year.

"We did make quite an early switch to next year's car, but that's not all of it," he said.

"Because some of the things we concentrated on at the start of the year to become our developments right through the year simply didn't work as well as expected.

"We just haven't met the targets."

Additional reporting by Jonathan Noble