Franz Tost has blamed Williams for costing BMW a championship and Ralf Schumacher the chance to win the only Formula 1 title of his career. Back in 2003, Williams were fighting with Ferrari and McLaren at the top of the Constructors’ Championship. Speaking to F1 Insider, Tost believes that BMW were at their very best that year, but one key mistake cost them the chance to win the title. The early 2000s was one of the most competitive periods in Formula 1 history. McLaren had recently won titles with Mika Hakkinen and Ferrari had just poached Michael Schumacher from Benetton. Williams were also …