The Henley's cantilever fabric-covered monoplane wing was mid-set, a retractable tail wheel landing gear was selected and accommodation provided for a pilot and observer/air gunner.

Although construction of the Henley prototype began in mid-1935, the Hurricane had priority, and it was not until 10 March 1937, powered by a Merlin "F" engine, that it first flew at Brooklands, shortly after the competing Fairey P.4/34.

Subsequently, the aircraft was refitted with light alloy stressed-skin wings and a Merlin I engine (the production version of the F) and further test flights confirmed a top speed of 300 mph (480 km/h), which met the RAF's requirements.

[citation needed] The second prototype was fitted with a propeller-driven winch to haul in a target tug's drogue cable after air-to-air firing sorties and first flew on 26 May 1938.

[citation needed] Unfortunately, unless the aircraft were restricted to an unrealistically low towing speed of 220 mph (350 km/h), engine failures was unacceptably frequent, which was attributed to the cooling system matching the Henley's original mission but inadequate when towing a target, with its substantial drag, which resulted in high engine speeds but low airspeed.