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Easy to say, with 20/20 hindsight; unfortunately the hierarchy didn't share the same prognosis. When Dowding demanded armour for his pilots, Sholto-Douglas said that, since the Spitfire was the fastest thing in the air, only an inattentive pilot would allow something to get behind him. If he didn't expect Spitfires to face the Me109, why would he think differently about the Defiant?That suggests a British army supported by British Defiants were part of the RAF unit tasked to support the BEF so it's reasonable to assume they would be fighting Me-109s.
What makes you think the Defiant would perform well in that role? I think Norway based Me-110s would eat it for lunch. The only saving grace is that Me-110 day fighters were few in number.
I never said the operational record would have been good, I said it might not have been so bad. The tactics Hunter developed comprised forming a defensive circle with each gunner protecting the area around the aircraft to his immediate rear. The circle would then descend to prevent fighters from attacking the exposed underside of the Defiants. Now, a defensive circle isn't a way to win a dogfight but it can reduce your own losses, hence my comment.