I know its a contentious point, but its not illegal to brake with your left foot in an Auto. I don’t commonly use my left foot to brake, I sometimes have used it in special circumstance regarding autohold and steep rises, or other uncommon events. But, I have a friend who drives an auto and they always drive two footed. Indeed you brake quicker using your left foot than the right foot. That’s because its closer to the brake pedal and you don’t have to lift off the accelerator and then move across. That’s a proven fact.
The problems seem to arise from people developing a heavy left foot on the clutch and then lacking sensitivity to brake appropriately. But, people swiftly get over that. Or so my friend tells me.
Anyone using an auto first time or after a long time should drive safely in what ever way suits them, just beware of riding the brake, even slightly and confusing the autobox. Keep your left foot off the brake unless braking if you use two feet.