The Supreme Court has held that in the context of whistleblowing and unfair dismissal, the reason for dismissal is not always that in the mind of the decision-maker.
In Royal Mail v Jhuti www.bailii.org/ew/cases/EWCA/Civ/2015/439.html the claimant’s line manager, motivated by her whistleblowing, presented the claimant to the senior manager considering her position as having inadequate performance. The senior manager decided to dismiss her on grounds of her performance. The Supreme Court held that the reason, or principal reason, for the dismissal was the whistleblowing.
This was not a case on direct discrimination under the Equality Act, but it remains to be seen whether the case influences future decisions on that.