Barcelona, Spain -  Brawn GP remain the team to beat after Jenson Button's fourth victory in five races, but there are signs of discord after a threat by team-mate Rubens Barrichello to quit Formula One if team orders come into play.

The Brazilian said in an interview he would quit if he believed championship leader Jenson Button was being favoured by the Brawn GP team.

"If I get the slightest sniff of the fact that they have favoured Jenson, I will hang up my helmet tomorrow," Barrichello told United States channel SpeedTV.

Button won the Spanish Grand Prix ahead of the Brazilian on Sunday, making it four victories in the first five races, to extend his lead at the top of the drivers' championship.

Button's victory came after a change of strategy from team boss Ross Brawn, reducing his planned pit stops from three to two.

Button made the most of a switch to win the race and move to 41 points in the standings, ahead of Barrichello (27) and Germany's Sebastian Vettel (23 in a Red Bull.

Barrichello was number two behind Michael Schumacher at Ferrari - when Brawn was technical director - and suffered from team orders which prevented him from racing the German.

"I have had experience of that and if it happens I won't follow any team orders," said Barrichello who left Ferrari in 2005.

"I'm making this clear now but we have a much more friendly situation in this team."

The British press meanwhile see Button already well on his way to the drivers' title.

"Another race, another win. It is almost getting boring now. Almost," the Telegraph wrote.

"Jenson Button's fourth victory in five Grands Prix may not have had the on-track fireworks of his previous three, but the aftermath hinted at something pretty explosive; the suggestion from his team-mate Rubens Barrichello of a potential rift brewing at Brawn GP."

The Times asked: "Who can stop Jenson Button now? After his fourth win in five races at the Spanish Grand Prix yesterday, which came at the expense of a disgruntled Brawn GP team-mate in Rubens Barrichello, the British driver looks set fair for a crushing World Championship victory this season.

"The only other question left is how many more races he is going to need to win to become the second Briton in succession, after Lewis Hamilton, to reach the pinnacle of motor racing."

Hamilton was left out of the points in a struggling McLaren-Mercedes and asking, "What can I do? I drove my heart out, as I always do, it's just that the car is not good. I had no grip."

Ferrari are just as frustrated despite Felipe Massa scoring his first points of the season with sixth place.

When asked whether he could still fight for the title, the Brazilian said: "I don't think this year. Maybe next year."

Team chief Stefano Domenicali said Massa's performance was a positive note to go to Monte Carlo for the May 24 Monaco Grand Prix.

"There is a lot of pain," he said.

"I would be dishonest if I didn't say there is a lot of pain, because that is the thing that I have now. It is important that, once again, we need to make sure that the people who have the responsibility in all the areas do the maximum job we can do."

Meanwhile in the continuing row over a proposed budget cap, Red Bull said it could pull out of Formula One at the end of the season over the plans.

Dietrich Mateschitz, the owner of the drinks company which backs the team and sister team Toro Rosso, has called on governing body FIA to change plans to introduce a 40-million-pound (61 million dollars) budget cap on each team.

"If the proposed rules for 2010 stay unchanged, we will not take part in the 2010 championship," Mateschitz told the Salzburger Nachrichten newspaper in an interview published on Monday.

Toyota's John Howett had said Sunday his team would also consider pulling out of Formula One racing if FIA insisted on the budget cap.

FIA boss Max Mosley and the team principals are to meet in London next week to discuss the issue. (dpa)