This design has been traduced because of misuse of the word "fighter". RAF/1930s bought no "fighter" because UK was to rely on the Maginot Line: Luftwaffe Army-support types - He.111/Do.17, transport-derived -would trundle beyond escort range towards Expeditionary RAF bases, to be taken out from below/astern after visual intercept. No GCI, no nightwork, on either side. Payload/endurance was sought: no single-engined type burdened by turret+its gunner could take on a nimble dasher: but Defiant would not meet one, short-range, immured beyond the Rhine.
Hurricane, Spitfire, Whirlwind, Bf.109, Bf.110 (Zerstorer) were similarly intended to be bomber-destroyers. Defence Policy has failed if our lot are within range of no-endurance, point-defence sprinters. RAF's 1936 name-change, Air Defence of G.B to Fighter Command was a budget-jerking wheeze: politicos wanted to concentrate spend on bombers.
cazatou's points re Gloster/Hawker: Air Ministry "owned" Design Rights in everything we paid for; design parents had no right to production. A.M left Defiant in BPA (and put Blackburn Roc there too, as BPA supplied the French-origin turret). BPA also built Hawker Demon and Fairey Barracuda; Gloster built 2,750 Hurricanes.