I think you'll find they are claims rather than confirmed kills - and a lot of those were on one day over Dunkirk.
"Although 264 Squadron claimed 48 kills in eight days over Dunkirk, the cost was high with 14 Defiants lost. Actual German losses were no more than 12–15 enemy aircraft; the turret's wide angle of fire meant that several Defiants could engage the same target at one time, leading to multiple claims."