The celebrated decision of the House of Lords in R v Tower Hamlets LBC, ex parte Chetnik Developments Limited (1988) AC 858 is justifiably well known for its robust affirmation of the principle that there is no such thing in public law as an unlimited or unrestricted discretion. Linked to this was the endorsement, at pages 874H-877Q, of the principle in Ex parte James (1874) L.R.9 Ch. App. 609 that a public body must act in a “straightforward”, “high-minded”, and “high-principled” way.
The principle in Ex parte James has now been considered by the Court of Appeal in Lehman Brothers Austria Ltd (In Liquidation) v Macnamara (2020) EWCA Civ 321. The threshold test for the invocation of the principle, on an objective basis, is “fairness”, procedural and substantive, rather than unconscionability, on the particular facts of a case; and the principle applies to reliance upon legal rights, including contractual rights: paragraphs 38, 64-69 inclusive, 87-90 inclusive, and 105/106.