RUBENS BARRICHELLO has threatened to quit Formula One if he senses team orders coming into play in his fight for the title with team-mate Jenson Button.

Jenson Button continued his dominance of this season's Formula One world championship today with his fourth win in five races after a superb pit-stop strategy switch at the Spanish Grand Prix.

Lewis Hamilton again raised hopes of a McLaren revival by topping the timesheets at the end of first practice for Sunday's Bahrain Grand Prix.