Firstly if the highway code does not reflect common, accepted practice then it is out of step, and likely to be ignored. I remember an architect saying, it is bad practice to set out the route of pathways on developments, the best thing to do is see which places the residents use as paths and then build a path there, otherwise they will rightly ignore your paths and make their own, more suitable ones. Secondly, if you get yourself into an accident by following another drivers signal it is still your fault, the first rule of driving is that you are in charge of the vehicle and it is firmly up to you to decide if something is safe to do, I doubt that if someone said 'of course you can jump off that cliff, it won't hurt you' that anyone in their right mind would take that advice.