In Gallaher Group Limited v Competition and Markets Authority (2016) EWCA Civ 719 the Court of Appeal considered the application of the EU and common law principle of equal treatment. Lord Dyson MR said, at paragraph 39: “In my view, the fact that one party (A) has made a request for more favourable treatment and another party (B) has not done so will rarely amount to a good reason for not treating them as being in a relevantly comparable position for the purposes of equal treatment if they are in fact otherwise in relevantly comparable positions”.
On the matter of objective justification for not replicating in favour of the appellants the approach adopted in relation to another because that approach had been mistaken, the question (paragraph 53) is whether the difference in treatment is “fair in all the circumstances”. “The fact that a decision by a public authority is mistaken is not a “trump card” which will always carry the day so as to permit the authority not to replicate the mistake regardless of the circumstances. … the question is whether there has been unfairness on the part of the authority having regard to all the circumstances. The fact that there has been a mistake may be an important circumstance. It may be decisive. It all depends.”
Lord Dyson continued, at paragraph 54: “The law relating to legitimate expectation is of some assistance here. It is well established that a legitimate expectation cannot be relied on to require a public authority to act in breach of its statutory duty or to do something ultra vires. … But the courts have considered whether a public authority may defeat a legitimate expectation where the expectation has been created by mistake. In R v Department for Education and Employment, ex p Begbie [2000] 1 WLR 1115, 1127B-D, Peter Gibson LJ said that, where the court is satisfied that a mistake has been made, the court should be slow to fix the public authority permanently with the consequences of a mistake. But importantly, he went on to say that the question of whether the authority should be permitted to resile from a mistaken statement depends on whether that would give rise to unfairness amounting to an abuse of power. The law relating to legitimate expectation is grounded in fairness.” Longmore and Lloyd Jones LJJ agreed.