Supreme Court confirms narrow limits to doctrine of issue estoppel

The Supreme Court has held that the Danish Customs and Tax Administration was not barred by issue estoppel from bringing new claims against the same defendant following the dismissal of its earlier claim under the rule which prevents English courts enforcing foreign tax claims. The new claims, which alleged fraud, were brought on different factual and legal bases from the original claims: Skatteforvaltningen v MCML Ltd (formerly EDFM) [2026] UKSC 19.

The decision emphasises that issue estoppel must be kept within very narrow limits, given its dramatic effect. In particular, where the doctrine applies, it may prevent an issue being contested in later proceedings between the same parties, even if the prior decision on that issue turns out to have been wrong in law. 

The judgment makes clear that, in order for an issue estoppel to arise, the following principles apply: 

• The issue decided in the prior proceedings must have been necessary and fundamental to the judgment in those proceedings. 
• In deciding whether an issue was necessary and fundamental for these purposes, the question of whether the issue arose on the parties’ pleadings in the prior proceedings is critical. 
• Only the immediate foundation of the ultimate decision can give rise to an issue estoppel. Elements of the prior court’s reasoning that simply led up to the decision cannot do so.

Accordingly, the fact that a judge frames their reasoning more broadly than was necessary to determine the case will not mean that a party is bound by an issue estoppel to that same broad extent. 

The decision recognises that there is an exception to issue estoppel where "special circumstances" arise, in particular where new material has become available since the decision in the prior proceedings. However, the Supreme Court did not have to consider whether the exception applied in this case, given its decision that the claims were not barred by issue estoppel. The "special circumstances" exception to issue estoppel is however considered, by analogy, in a more recent Supreme Court decision in the context of group litigation orders, Axa Insurance UK Plc v Commissioners of Inland Revenue [2026] UKSC 24. See our blog post on that decision here.

Background

Skatteforvaltningen (SKAT) is the Danish Customs and Tax Administration. EDFM was a financial brokerage business. At the relevant time, Danish law imposed a tax on dividends paid by Danish companies. This operated on a withholding basis, meaning that a Danish company was obliged to pay a percentage of the dividend to SKAT as withholding tax, with the balance then being distributed to shareholders. Some non-Danish shareholders were entitled under double taxation treaties not to be taxed on Danish dividends and could therefore claim refunds of the withholding tax that had been deducted. EDFM issued tax vouchers to clients which were then used to support applications to SKAT for tax refunds. 

The 2018 claim 

In 2018, SKAT brought a claim (the 2018 claim) against more than a hundred defendants, including EDFM. SKAT alleged that EDFM was liable for negligent misrepresentations contained in tax vouchers that it had issued. EDFM’s clients had then used these vouchers to apply for refunds to which, SKAT argued, they were not entitled. 

At first instance, all of the claims were found to be inadmissible under the conflicts of law rule (the Revenue Rule) which prevents an English court from hearing a claim brought by a foreign state to enforce its tax laws. SKAT successfully appealed this decision against various defendants, with the Court of Appeal finding that the claims were not barred by the Revenue Rule and that the first instance ruling in this regard was wrong in law. However, SKAT did not challenge the finding regarding the Revenue Rule against EDFM. It instead pursued a different, limited ground of appeal, which failed. This meant that the finding between SKAT and EDFM that the Revenue Rule barred SKAT’s claim was final.

The 2022 proceedings 

In 2022, SKAT brought new claims against EDFM, this time alleging fraud rather than negligence (the 2022 claim). The 2022 claim covered many of the same tax vouchers already considered in the 2018 proceedings, and five new vouchers.

EDFM applied to strike out the 2022 claim, arguing that it was an abuse of process and barred by issue estoppel. 

The strike-out application was refused at first instance, on the basis that the 2018 and 2022 claims were different claims involving different causes of action and different factual allegations, so no issue estoppel arose. On appeal, however, the majority in the Court of Appeal held that issue estoppel applied. 

The majority (Newey and Popplewell LJJ) considered that the issue determined in the 2018 proceedings was that all private law claims to recover withholding tax refunds paid out by SKAT based on applications conveying incorrect information were inadmissible under the Revenue Rule. As framed, this issue also covered the claims based on the new tax vouchers. Nugee LJ took a different approach, considering that the issue identified by the majority could not give rise to an estoppel because it was a general proposition of law untethered to any particular facts, and a party could only be estopped by a judge’s conclusion on the facts of a particular case. In his view, the scope of the estoppel was to be defined by reference to the transactions common to both the 2018 and 2022 claims but did not extend to the five new vouchers.

SKAT appealed to the Supreme Court. 

Decision

The Supreme Court unanimously allowed the appeal. Lord Sales and Lord Doherty gave the lead judgment, with which Lord Lloyd-Jones, Lady Rose and Lady Simler agreed. 

The principles

The court observed that issue estoppel has a very powerful effect. It can restrict or deny a litigant's access to court to vindicate what is otherwise a good claim, or prevent them from raising what is otherwise a good defence. It is therefore a serious interference with the ordinary right of litigants to present their claims and to defend themselves, and the courts have been astute to keep the doctrine within narrow limits.

The legal effect of an issue estoppel reaches further than the doctrine of precedent. The latter obliges courts to follow the ruling of an appellate court on a particular point of law, but a litigant in subsequent proceedings (even if they were a party to the earlier proceedings which established the precedent) can seek to distinguish it or persuade a court to overrule it. There is no such possibility with issue estoppel, subject to a narrow exception for special circumstances (ie where further relevant material has become available which could not by reasonable diligence have been adduced in the previous proceedings). The court considered there to be no sound reason to give issue estoppel as wide an ambit as the doctrine of precedent.

The court outlined the following legal principles, which it considered to be well established: 

1. The issue decided in the prior proceedings must have been necessary and fundamental to the decision in order to give rise to an issue estoppel. 
2. In deciding whether an issue was necessary and fundamental, whether the issue arose on the parties’ pleadings is critical. 
3. It is only the immediate foundation of the ultimate decision which can give rise to an issue estoppel. Elements of the court’s reasoning which led up to the decision cannot do so. 

One reason why the scope of an issue estoppel is limited to the immediate foundation of a decision is because it would be unjust for a party to be estopped where elements of the prior court’s reasoning went wider than was necessary to determine the case. The scope of issue estoppel should not depend on how widely or narrowly a judge chose to frame their reasoning.

Moreover, the time and effort a party can be expected to invest in litigation depends on context and the value and importance of particular points arising. Litigants should be neither expected nor incentivised to spend time and effort litigating points which were not important to the first set of proceedings just in case they become relevant in later proceedings. It would therefore lead to injustice if the doctrine of issue estoppel were found to apply where a party could have put some point in issue but chose not to do so. Any unfairness where a party seeks to raise a point it could have raised in previous proceedings is instead controlled by the law on abuse of process, which operates more flexibly.

A further reason for confining the operation of issue estoppel within narrow limits was that it would otherwise displace the operation of the doctrine of precedent. The latter was developed to strike a balance between the need for certainty and predictability in the law, through authoritative guidance from appellate courts, and the desirability of doing justice in the particular case, by applying the relevant law to that case. Applying the doctrine of issue estoppel too widely would undermine that balance.

Such considerations underpinned the emphasis on the narrow operation of the doctrine of issue estoppel. The scope of an issue estoppel was not to be enlarged by inference, deduction, or argument from the prior decision. An issue estoppel arising from a decision on one set of facts should not be expanded to cover another set of facts, even if the factual differences were not material in law to the prior court's decision. 

Application to the facts

What was in dispute in the 2018 claim was whether the statements made in the tax vouchers were negligent misstatements, and if so whether they fell within the Revenue Rule. What was in dispute in the 2022 claim was whether the statements set out in various of those vouchers (and five further vouchers) were fraudulent misstatements, and if so whether they fell within the scope of the Revenue Rule. These matters were not addressed in the 2018 proceedings. The factual and legal bases of the 2022 claim were not the same as the 2018 claim, and were not pleaded in the 2018 proceedings. 

In the 2018 proceedings, the judgment was that the claim as alleged was in substance a claim for tax which fell to be dismissed by reason of the Revenue Rule. The issue stated by the majority in the Court of Appeal was much wider, extending to all private law claims to recover withholding tax refunds paid by SKAT based on applications conveying misinformation. That broader issue was not necessary or fundamental to the decision in the 2018 proceedings and was not the immediate foundation of it. The majority in the Court of Appeal therefore wrongly expanded the scope of the issue estoppel arising from the 2018 claim to cover another different set of facts. Nugee LJ’s formulation of the issue suffered from the same difficulties.

The Supreme Court therefore allowed the appeal, holding that the 2022 claim should not have been struck out.