Sadly,not so much of Gun Camera evidence lives today.
I have however had the fortune of looking through their archives at the IWM in London. Cool films of P51's shredding 190's, and Tempests shredding trucks.
There were some from the BoB there as well, so they must have been used.
After revising the true scores of the BoB, Fighter command did not accept claims for a kill unless the enemy aircraft either had a bailout, disintegration, or a crash landing, - witnessed or filmed.
That suggests that gun cams were either not fully reliable or not standard equipment everywhere in the BoB.