Per Rem Judicatam in UK Law

If in litigation upon one such cause of action any of such separate issues as to whether a particular condition has been fulfilled is determined by a Court of competent jurisdiction, either upon evidence or upon admission by a party to the litigation, neither party can, in subsequent litigation between one another upon any cause of action which depends upon 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.

The determination by a Court of competent jurisdiction of the existence or non-existence of a fact, the existence of which is not of itself a condition the fulfilment of which is necessary to the cause of action which is being litigated before that Court, but which is only relevant to proving the fulfilment of such a condition, does not estop at any rate per rem judicatam either party in subsequent litigation from asserting the existence or nonexistence of the same fact contrary to the determination of the first Court.

On an appeal (which is a re-hearing) we have said that the fresh evidence must be such that, if given, it would probably have an important influence on the result of the case, though it need not be decisive, see Ladd v. Marshall (1954) 1 Weekly Law Reports at page 1491 and Skone v. Skone (1971) 1 Weekly Law Reports at page 815. But in order to avoid the effect of an estoppel (when there is no re-hearing) the fresh evidence must, I think, be decisive.

The first principle is that once a cause of action has been held to exist or not to exist, that outcome may not be challenged by either party in subsequent proceedings. Fourth, there is the principle that even where the cause of action is not the same in the later action as it was in the earlier one, some issue which is necessarily common to both was decided on the earlier occasion and is binding on the parties: Duchess of Kingston's Case (1776) 20 St Tr 355.

Res judicata is a rule of substantive law, while abuse of process is a concept which informs the exercise of the court's procedural powers. In my view, they are distinct although overlapping legal principles with the common underlying purpose of limiting abusive and duplicative litigation. That purpose makes it necessary to qualify the absolute character of both cause of action estoppel and issue estoppel where the conduct is not abusive.

Cause of action estoppel arises where the cause of action in the later proceedings is identical to that in the earlier proceedings, the latter having been between the same parties or their privies and having involved the same subject matter. In such a case the bar is absolute in relation to all points decided unless fraud or collusion is alleged, such as to justify setting aside the earlier judgment.

I consider that anyone not possessed of a strictly legalistic turn of mind would think it most unjust that a tenant should be faced with a succession of rent reviews over a period of over twenty years all proceeding upon a construction of his lease which is highly unfavourable to him and is generally regarded as erroneous. Estoppel per rem judicatam, whether cause of action estoppel or issue estoppel, is essentially concerned with preventing abuse of process.