Both the UK's immediate postwar 4-engined prototypes were lost shortly after takeoff on test flights due to controls being misassembled.
The Handley Page Hermes prototype crashed on its maiden flight in December 1945, killing the key Handley Page test pilot team, due to the elevators being misconnected.
The Avro Tudor prototype crashed in August 1947, killing among others the Avro chief designer, Roy Chadwick, who had designed the Lancaster, the Tudor itself, and various other Avro types. The aileron cables had been reversed following overnight work.