Yes, an employee has the right to be accompanied by a work colleague or trade union official (even if the company does not recognise a trade union). Please see the sample grievance procedure for further guidance.

Yes, an employee does have the right to appeal against a grievance outcome. You should set out their right to appeal in the outcome letter, advising who to contact and in what time frame.  See the sample policy that recommends 5 days from receiving the outcome as an appropriate amount of time.

You should still meet with the employee to ascertain the reasons for their informal grievance and how their issues might be resolved. Depending on the nature of the grievance, even if they do not wish to raise it formally, you may still need to follow the grievance investigation procedure.