What is the test for issue estoppel?

In the case of Thoday v. Thoday, [1964] 1 All E.R. 341 at p. 352, Lord Diplock explained the doctrine of issue estoppel in these terms: The second species [of res judicata], which I will call "issue estoppel", is an extension of the same rule of public policy [that a person should not be vexed twice for the same cause of action]. There are many causes of action which can only be established by proving that two or more different conditions are fulfilled. Such causes of action involve as many separate issues between the parties as there are conditions to be fulfilled by the plaintiff in order to establish his cause of action; and there may be cases where the fulfilment of an identical condition is a requirement common to two or more different causes of action. If in litigation on one such cause of action any of such separate issues whether a particular condition has been fulfilled is determined by a court of competent jurisdiction, either on evidence or on admission by a party to the litigation, neither party can, in subsequent litigation between them on any cause of action which depends on the fulfilment of the identical condition, assert that the condition was fulfilled if the court has in the first litigation determined that it was not, or deny that it was fulfilled if the court in the first litigation determined that it was. (Emphasis mine.)