Introduced in 1926, Percy Riley’s 9hp, 1,087cc, twin-camshaft four was an outstanding engine design by any standards, various versions powering Rileys until 1957.

Clothed in stylish bodywork by Stanley Riley, the Coventry marque’s pre-war offerings were among the world’s finest small-capacity sporting cars.

Right from the start it was obvious that the 9hp Riley engine possessed enormous potential as a competition unit, and at Brooklands J G Parry-Thomas and Reid Railton were the first to demonstrate just how good it was.

The success of their racer led to a production version, the Speed Model, which soon became known as the Brooklands Nine.

Six-cylinder Brooklands and MPH models followed, and from these Riley developed the next of its 9hp four-cylinder sports cars – the Imp.

Like the MPH, the Imp featured a short-wheelbase chassis, of 7’ 6” in the latter’s case, that swept upwards over the front axle and was under-slung at the rear, this layout having been first used on the Brookla...