The new design, given the company designation B.48, was known unofficially by Blackburn as the "Firecrest" but was always known by S.28/43, the Air Ministry specification. It was a low-winged, single-seat, all-metal monoplane. Aft of the cockpit the fuselage was an oval-shaped stressed-skin semi-monocoque, but forward it had a circular-section, tubular-steel frame.
The newly designed aircraft, assigned the company code B.48, was informally referred to as the "Firecrest" by Blackburn but retained its official designation S.28/43 under Air Ministry guidelines. The monoplane had a distinctive low-wing design with an oval-shaped rear fuselage and a circular-section frame at the front.