The Arnold v National Westminster Bank exception permitting reopening of estoppel where new material becomes available that could not have been discovered with reasonable diligence does not apply to cause of action estoppel (true res judicata). For true res judicata, the bar is absolute and the court is restricted to examining the plaintiff's pleadings and the court's orders. The ground on which an earlier claim failed is irrelevant; only the result matters.
The full text is available to signed-in members, including the 12 later cases that cite this judgment.
1 of the 12 citing cases carry a classified treatment. How each court treated it is available to signed-in members.