IIRC, gun camera is only activated when the gun trigger is pressed. So, control around dicking pilots are just as good as knowing that they don't shoot friendly targets?
I actually kinda think of the enemy killing footage is more valuable as propaganda material than anything else.
In desperate Battle of The Britain times, when the whole British isles is under threat of starvation due to U-boot threat, and luftwaffe bombers, materials are in alarming shortage for the whole population. So I can't really imagine that the RAF dared to request film rolls to be imported from the US for all of its several hundred fighters, along with primary goods like food rations, raw materials, and other needs of those including the Royal family and the nobles.
But I heard that not all fighters are equipped with gun cams, is that true?