At Silverstone both of the works P83s suffered suspension failures in practise, and as a result Stewart took over the Reg Parnell P83 of Irwin, who in turn was given the P261 of Piers Courage, who had to sit out the race.
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The last non-championship race for the car was the International Trophy at Silverstone, Stewart driving the P83 while Spence was in a P261.