The Handley Page H.P.31 was a two-seat single-engined biplane built to a British specification for a carrier-based torpedo bomber and reconnaissance aircraft.

[1] It was powered by a single water-cooled Napier Lion engine, initially a 470 hp (350 kW) mark V, mounted as low in the nose as airscrew ground clearance allowed so that the top of the fuselage could fall away in front of the cockpit for the best views during high-incidence carrier landings.

The observer/gunner's position was close behind the pilot for ease of communication, since he had to do the work of navigation on long flights away from the carrier that had been traditionally assigned to a third crew member.

The main legs were attached to the front spar at the ends of the centre section, and pairs of bracing struts ran from the stub axles to the lower fuselage longerons.

By the spring of 1927 it was clear that the Blackburn Ripon was preferred, and in June the second prototype was returned to Handley Page rather than going forward to the seaplane trials, chiefly because of its persistent overheating.

Nonetheless, Handley Page gained funding for a Harrow Mk II using a more powerful Napier Lion XI engine producing 530 hp (395 kW) in the first prototype airframe.

At the same time drag was reduced and rudder and elevator lightness improved by lowering the rear fuselage decking and with it the gunner's position.

[1] During late summer 1927, the second prototype had been involved in continuing the series of Air Ministry tests of slats previously conducted on the Hendon III.