Webber: rival engines have caught up

The Cosworth unit was widely regarded as the best engine of the field when the season began, allowing Williams to fight at the top of the field.

But Webber believes the American engine supplier has been unable to keep up with the development rate of their rivals due to the smaller budget.

"At the start of the year we did have the best engine in the field. No doubt about it," said Webber before autosport.com revealed Williams will switch to Toyota engines next season.

"Now we have an engine that is equal to the opposition, I would say. At the start of the year that was a huge advantage for us and we started off strong.

"It's not possible for Cosworth to sustain that strength of development and budget against a Honda or Renault or Mercedes. But they have some very, very clever guys and they've actually held the fight up quite well.

"Okay, we've had an engine penalty and some failures in the races. On the Grove side, we should have no excuses."