"In terms of the difference in treatment between the claimant and Mrs Graham, we are satisfied that the respondent was entitled to distinguish them in the way that they did and that there is not any disparity of treatment between them that is unreasonable in the sense that the decision to reinstate Mrs Graham creates any unfairness to the claimant. It doesn't do so. However, we are satisfied that the disparity in treatment between the claimant and Mrs Saunders is wholly irrational and wholly undermines the third limb of Birchall."