“courts, including this court, do not often overturn settled rules of law, and in considering whether to do so they attach particular importance to the security of settled transactions. The decisions in Kleinwort Benson and Sempra Metals were exceptional in their readiness to overturn centuries of authority, as the House of Lords enthusiastically adopted the theory of unjust enrichment. Those decisions were criticised by this court in Prudential at para.63 because of their disregard of the need for judicial development of the law to be justifiable by reference to existing legal principles. Normally, as was stated in a recent judgment of this court, ‘[i]n order to preserve legal certainty, judicial developments of the common law must … be based on established principles, building on them incrementally rather than making the more dramatic changes which are the prerogative of the legislature’: R (Elgizouli) v Secretary of State for the Home Department [2020] UKSC 10; [2020] 2 WLR 857, [170].”