In England certainly the person supervising a learner driver is subject to the same laws about alcohol, mobile phone use, etc as someone actually driving- and can be convicted on a charge of aiding and abetting any crime the learner driver commits. This is the case regardless of whether they are a professional driving instructor with their own brake pedal, or a parent supervising their child driving the family car.
In Portugal there is an interesting law regarding this: The instructor/examiner is always liable for an accident during driving lessons/exams, except if the accident resulted from an action where the learner disobeyed a direct order by the instructor. In that case the learner takes responsibility.