I ALWAYS overtake or wait. I will never undertake. Why?
Car drivers always check their right mirror, they check their inside mirror usually (if at all) for left hand turns. Think about it. I check my inside mirror as I also cycle on the road- dont expect other drivers to.
Plus, when you overtake and filter back across infront of drivers- they’ve clocked you and mentally noted they are near a cyclist. It all helps.
Bad habits mean driver tend to use the outside mirror more- its common sense to play to this.
Undertaking (like fast driving) saves you what? 5mins on your journey?! Scraping along in the gutter at times etc- **** that.