Nevertheless, the team persevered and fitted a standard 1.5-litre Climax 4-cylinder engine, mounted at a slant to make room for the front driveshaft.

In addition the driving position was moved slightly off-centre to accommodate the gearbox and rear driveshaft to the driver's left hand side.

In the British Grand Prix at Aintree, Fairman drove the car again, but surrendered it to Stirling Moss after his Walker-entered Lotus 18 failed.

The P99's final competition action during this period came in the British Hillclimb championship in 1964, 1965, and 1966, with Peter Westbury winning the title in 1964.

In a 1997 interview for Motor Sport magazine, Sir Stirling Moss nominated the P99 as his favourite of all the F1 cars he drove.