When it comes to disciplinary investigations, an employers must act fairly and unbiased and investigate with an open mind. What exactly that means in practice depends, as always, on the circumstances, the nature of the misconduct, the resources the employer has and the possible outcome of the investigation. The Court of Appeal has now (not surprisingly) confirmed that only substantive fairness and an even-handed approach is required, not an in-depth forensic investigation. In the case at hand, the Court held for instance that the witnesses did not have to be interviewed all in the same manner.
Still, employers are well-advised to conduct interviews as similar as possible to be able to identify inconsistencies easily and to not even have an argument about differences in approach. After all, its not that hard either to follow the same process for every witness.