Rubens Barrichello has insisted that he and Brawn GP team-mate Jenson Button would fight clean and fair for the world championship.

Following Barrichello's stunning victory at the European Grand Prix in Valencia last Sunday just 18 points separate the veteran Brazilian from the pace-setting Button.

With the challenge from the Red Bull pairing of Mark Webber and Sebastian Vettel beginning to fade, 37-year-old Barrichello is determined to reduce Button's advantage at this weekend's Belgian Grand Prix in Spa.

“I'm closing in, it is a good moment for me,” he said. “Eighteen points is still a little too much but it is better than the 26 it was before Valencia.

“I'm driving well, I've been qualifying quite well, so I just need to build the best momentum to keep going.”

In practice this afternoon, Button and Rubens Barrichello were in 17th and 18th place — nearly a second off the pace set by McLaren's Lewis Hamilton, who topped the time sheets in 1min 47.201sec.

However, it was believed the Brawn drivers were concentrating on achieving optimum race settings for Sunday.

Although the title race is hotting up Barrichello claimed he and 29-year-old Button would compete like gentlemen, unlike other team-mates have in the past.

Title fights turned ugly between the late Ayrton Senna and Alain Prost at McLaren, and Nigel Mansell and Nelson Piquet at Williams. But Barrichello said: “Jenson and I respect each other. He is a great driver.

“We are working well and are not looking like we are going to clash on the racing track. May the best man win.”

Webber, who celebrated his 33rd birthday yesterday, maintains he is among the best men on the grid. But the Australian, third in the championship 20.5 points behind Button, acknowledged the chances of beating either his British rival or Barrichello to a maiden title are now slim.

“It's Brawn's to lose, we know that,” he said.

“They are the hunted but we have to gain a lot on them. It's not impossible but I know it's going to be tough.

“We need a phenomenal amount of points and a very consistent run and even then we need to have both of the Brawns to have a rough run.”

That view was echoed by Red Bull chief Christian Horner, who conceded that Sunday's Grand Prix could be pivotal for Webber and German team-mate Vettel, who is 25 points adrift of Button.

Horner said: “I wouldn't say the championship is over but this is a key weekend for us. We need a big points score here.”

Meanwhile, McLaren principal Martin Whitmarsh moved to dispel rumours sweeping the paddock at Spa that Renault's Fernando Alonso was set to rejoin McLaren with whom the two-times world champion endured such an acrimonious relationship in 2007.

Whitmarsh said: “Fernando is a great driver, but I don't think he will be coming back to us quite so soon.

“Certainly, I haven't spoken to Fernando or his management about a return.”