Jenson Button impressed by former team Williams

Button is now with McLaren after starting out life in the sport at Williams - amassing 12 points from 17 races in 2000.

With one podium finish to his name this term, Button has helped McLaren to sixth in the constructors' standings - 38 points and two places behind Williams.

Drivers Valtteri Bottas and Felipe Massa have taken Williams to just outside the top three, although Button is not surprised by the results of his former team.

"I think they've put a lot of effort into doing well this year. They've spent a lot of resources on getting a good team of people, especially aerodynamically," Button told AUTOSPORT.

"They've done a great job and I'm happy for [founder] Frank and [deputy team principal] Claire [Williams] to see them competitive."

Williams' impressive form since beginning their use of the Mercedes engine could have been improved further were it not for a number of unfortunate incidents so far this campaign.

Massa has been forced into retiring during three races this season - limiting his contribution to 40 points - and Button joked their misfortune had been a blessing for McLaren.

"They've lost a lot of points this year through incidents or just not getting everything out of the car, which is good for us, because otherwise they'd be miles in front," he added.

"Their main aim is going to be being consistent and doing a good job as a team over the race weekend, because they've got the package to be very quick.

"It's just whether they can get the best out of it."