The appeal in NASIR v ZAVARCO plc (2025) UKSC 5 concerned the scope of the longstanding English law doctrine of merger. In short, the question is whether the doctrine, by which a cause of action merges with a judgment in the action, applies to a declaratory judgment. The Supreme Court held that it does not.
The doctrine of merger was developed as a means to promote finality in litigation and to prevent duplicative and vexatious litigation. Unlike the standard defence of res judicata in the form of cause of action estoppel, which prevents the contradiction of an earlier judgment as to the existence or non-existence of a cause of action, merger was designed to make a litigant seek his or her remedies in one action by extinguishing a cause of action when judgment has been given on it.
Lord Hodge examined the early historical development of the doctrine of merger, statutory intervention and modern case law, and what is the cause of action that merger extinguishes. He observed at paragraph 37 that:-
“In the context of the doctrine of merger, in my view, the concept of a cause of action which is extinguished by the obtaining of a judgment involves the right to a remedy in the given factual circumstances …”
He continued at paragraph 39 as follows:-
“There is no English case law authority on the application of the doctrine of merger to declaratory relief. The cases on merger to which I have referred all concerned attempts by claimants to pursue fresh proceedings after having obtained a judgment for the payment of a sum of money or to enforce a right of property by ordering the return of property. In this judgment I use the expression “coercive judgment” to describe such judgments for the payment of money or the return of property.”
At paragraph 44 Lord Hodge said:-
“There is no authority which supports the extension of the doctrine of merger to cover the declaration of the existence of a right and there are good reasons why the doctrine should not be so extended.”
At paragraph 45 he said:-
“… the doctrine of merger was developed and fully formed before the courts adopted the practice of giving purely declaratory relief and it is striking that in more than a century since the grant of purely declaratory relief became more widespread there is no example in case law of the doctrine of merge being applied to such relief.”
From paragraph 49 he concluded:-
“49. In my view Spencer Bower was and is correct to confine the established application of the doctrine of merger to coercive judgments and thereby exclude declaratory relief from its ambit. I would however reserve judgment on whether the doctrine extends to final injunctions so that the grant of a final injunction enforcing a right would preclude a later claim to damages arising from the same facts. That is a matter on which the court has not been addressed and there may be arguments against applying the doctrine to such orders.
- …a declaration is a quite different remedy from judgment for a debt or damages. It makes sense to speak of a merger of a claim for a debt or damages into a judgment for the payment of a specified sum as debt or damages, so creating ‘an obligation of a higher nature’. The lesser right is merged into the higher. The same simply cannot be said of a purely declaratory judgment, which itself imposes no obligation but only confirms the obligation which already exists…
- Secondly, there may be justifiable reasons for a litigant to seek a declaration before pursuing a claim for a coercive remedy…
- Thirdly, the doctrine of merger has often been criticised for its rigidity and its capacity to cause injustice… That possibility of injustice is a relevant consideration against extending the doctrine of merger to circumstances in which it has not been applied and in which it would be incongruous.
- Fourthly, to allow a claimant to obtain a purely declaratory judgment without excluding its right thereafter to seek a remedy such as damages does not give rise to the mischief of duplicative or vexatious litigation, or at least to the extent of a repetition of a trial on its merits …
- Fifthly, … there are currently a range of rules and remedies by which a court can achieve finality of litigation and prevent duplicative and vexatious suits, and the modern powers of case management enable the court to control the conduct of a litigation to promote efficiency and the proportionate use of resources. There is no need to extend the scope of the doctrine of merger to remove a lacuna.”