The airline had a requirement, which was translated into Air Ministry specification 21/28, for a mailplane to carry a 1,000 lb (454 kg) payload on a 1,000 mile (1,609 km) leg at a reasonable speed. Boulton & Paul designed and constructed the prototypeP.64 Mailplane to address these requirements. The aircraft (registered G-ABYK) first flew in March 1933 at the company Norwich. It was not a success, deemed to be expensive and unsatisfactory. It was destroyed during trials at Martlesham Heath when it struck the ground during an unexplained dive on 21 October 1933.
The company then addressed the specification's requirements with a new design transport aircraft which was lighter, slimmer and longer (the Boulton Paul P.71A).