 Complete the following phrase:  Rolt competed in three Formula One World Championship races, the British Grands Prix of 1950, 1953,  1955, but all three outings ended in retirement. At the 1950 British Grand Prix, the first-ever round of the F1 World Championship, he started 10th on the grid in an ERA that had been qualified by Peter Walker, but the gearbox failed after four laps. In the 