I can reach the fuel selector of a PA-28 from the right! Obviosuly as an instructor I ask the student, unless flying with an especially pretty girl
It is certainly not illegal to do so in the UK. While burning off hours for pre-course requirements of my FI(R) I asked my instructor / head of training if I could fly from the right (with a qualified CPL pax, as it happened, for practice in preparation for the FI course) and he said it was perfectly alright, and that was on the company insurance.