In this UK case on how much control a claimant might have over the individual person accompanying an employee to a disciplinary or grievance process, the E&W High Court has held that the University’s refusal to allow Professor Stevens to be accompanied at an investigation meeting by his medical defence union representative amounted to a breach of the duty of trust and confidence, notwithstanding collectively-agreed procedures and statutory provisions that restrict the accompanying person to either a colleague or trade union representative.
http://www.bailii.org/ew/cases/EWHC/QB/2015/2300.html 

The manner in which disciplinary investigations are conducted is of significant importance to employer and employees alike. For an employee it is critical that a disciplinary investigation is conducted fairly and objectively as experience tells us