Why heavier fighter cannon took time to field

Why did Britain not field heavier cannon armament on fighters sooner?

The demand existed, but cannon first had to be made reliable in the cold and icing conditions of high-altitude combat.

A viewer asks why the bomber threat did not produce heavier fighter armament sooner. The RAF and Fleet Air Arm did push for more powerful weapons. The immediate technical problem was keeping cannon warm enough to fire reliably at high altitude without icing, while Browning machine guns already worked across the required height range. Once the Hispano installation overcame that problem, the services deployed cannon as quickly as they could.