If the burden of proof reverses in a discrimination case, the employer has to show a non-discriminatory reason for the treatment about which the complaint has been made. Sometimes this is straightforward but the decision of the Employment Appeal Tribunal in Arhin v Enfield Primary Care Trust provides an example of a situation where it can be more difficult. It was found that the respondent had simply made a mistake in not allowing the claimant, who was redundant, to compete for a job that was offered to her comparator. However, the tribunal had failed to adequately explain how it had reached this conclusion in circumstances in which it admitted that there was insufficient evidence of the scope of the new role.

In his judgment, Justice Langstaff also makes some general observations about cases in which mistake is argued as the reason for less favourable treatment. While, of course, it will occasionally be true that a mistake has been made, and this will always be a satisfactory reason which discharges the burden of proof, tribunals are entitled to be suspicious of such an explanation, especially where it has not been pleaded and emerges for the first time in oral evidence. It is easy to allege and so must be submitted to close scrutiny. This necessarily requires a tribunal to make detailed findings about how it happened.