The Supreme Court’s recent decision in Skatteforvaltningen v MCML Ltd [2026] UKSC 19 is a welcome restatement of the scope of issue estoppel and provides useful guidance on its interaction with abuse of process. Although the judgment arises from long-running litigation concerning an alleged Danish Cum-Ex dividend tax fraud, it is of broader significance to English civil litigators. Anastasia Nourescu and Adam Jacobs review the decision.
In their joint leading judgment, Lord Sales and Lord Doherty, with whom the rest of the court agreed, rejected the Court of Appeal’s more expansive approach to issue estoppel. They reaffirmed that the doctrine should be applied restrictively, as a narrow exception to the general principle that parties should be able to bring or defend claims without undue constraint. The court also clarified that abuse of process remains the more flexible, and often more appropriate, mechanism for controlling improper repeat litigation.
For claimants, the decision confirms that the failure of one cause of action will not necessarily bar subsequent private law claims arising from the same facts, unless the earlier decision necessarily and fundamentally determined an issue that precludes the later claim.
Background
The proceedings form part of wider litigation by SKAT, the Danish tax authority, to recover Danish withholding tax refunds allegedly paid as part of a large-scale Cum-Ex fraud. In the 2018 proceedings, SKAT sued 114 defendants, alleging fraudulent misrepresentation against some and negligent misrepresentation and restitution against others, including MCML. The alleged misstatements arose from tax vouchers provided to SKAT in support of refund applications which, SKAT said, should not have been paid.
At first instance, Mr Justice Andrew Baker struck out all of SKAT’s claims under the Revenue Rule, which prevents the English courts from entertaining claims to enforce the revenue laws of a foreign state. SKAT succeeded on appeal against the alleged fraud defendants, but not against MCML and the other non-fraud defendants.
In 2022, SKAT brought fresh proceedings against MCML, this time on the basis that MCML had fraudulently prepared tax vouchers to induce the payment of refunds. The new claim concerned 286 vouchers, including 281 that overlapped with the 2018 proceedings and five new ones. Mr Justice Bright held that the claim was neither an abuse of process nor barred by issue estoppel.
The Court of Appeal agreed that the 2022 claim was not abusive, but a majority held that it was barred by issue estoppel. Specifically, they characterised the earlier decision as having determined that all private law claims against MCML to recover withholding tax refunds paid on the basis of applications conveying misinformation fell within the Revenue Rule. On that basis, SKAT could not avoid the rule by recasting its claim in fraud. That conclusion also caught the five new vouchers.
The issue for the Supreme Court was therefore whether the earlier Revenue Rule decision had necessarily and fundamentally determined an issue that precluded SKAT’s 2022 fraudulent misrepresentation claim, or whether the Court of Appeal had extended issue estoppel beyond its proper limits.
Issue estoppel remains a narrow doctrine
The Supreme Court’s central message was that issue estoppel must remain tightly confined. It is not enough that the later proceedings arise from the same factual matrix, or that reasoning in an earlier judgment might suggest the same outcome.
The test is more exacting: was the issue both necessary and fundamental to the earlier decision, assessed by reference to the pleadings? In other words, was it an indispensable foundation of the judgment, rather than merely part of the judge’s reasoning? The court stressed that this pleading-based analysis keeps the doctrine narrow: an estoppel can arise only in respect of the particular claim brought or defence raised.
On that basis, the Court of Appeal had been wrong to find an issue estoppel in this case. The 2018 claim against MCML involved allegations of negligent misrepresentation and restitution. In dismissing that claim under the Revenue Rule, the court had not needed to decide, or make any assumption about, whether a differently pleaded claim in fraudulent misrepresentation would also be barred.
Different causes of action remain available
The court’s reasoning turned on the 2018 pleadings and the legal quality of the facts the earlier court had to decide, ie, whether SKAT’s negligent misrepresentation and restitution claims, as pleaded, fell within the Revenue Rule.
In doing so, the court drew a helpful contrast. If MCML had denied that the alleged misstatements were made at all, and the earlier court had decided that point, SKAT would have been estopped from later alleging that the same misstatements had been made, whether negligently or fraudulently. However, that was not what the 2018 proceedings had determined.
That approach reflects the reality of complex commercial litigation. The same conduct may give rise to claims on a variety of bases, including in contract, tort, equity, or restitution, each with different ingredients and different factual or legal questions. The failure of one route should not, of itself, prevent the court from determining the issues required for another.
The relationship between issue estoppel and abuse of process
The court observed that issue estoppel is a rigid doctrine; if it applies, the parties are bound by the earlier decision, even if it was wrong. Abuse of process is different. It is a flexible and carefully modulated tool intended to prevent a party from raising a claim or defence that could (and should) have been advanced earlier.
The Supreme Court’s concern was that the Court of Appeal’s broader approach would blur that distinction. Treating reasoning or broad propositions from an earlier judgment as binding risked allowing issue estoppel to supplant abuse of process, undermining the latter’s sensitivity to fairness, context, and procedural history.
That was particularly important because both Mr Justice Bright and the Court of Appeal had already held that SKAT’s 2022 claim was not abusive, having considered why the fraud allegations were not advanced in the 2018 proceedings. To bar the claim through an expanded issue estoppel would have allowed a rigid rule of preclusion to override the fairness-based assessment designed precisely for that situation.
Practical implications
The decision provides useful clarity for litigants in successive proceedings arising from the same events. It restores issue estoppel to its orthodox limits and confirms that parties should not be deprived of legitimate claims that have not, in substance, already been determined.
That said, the judgment should not be read as licence to delay. Parties may understandably be cautious about pleading fraud, given the evidential threshold and potential costs consequences. However, where there is a reasonable basis for advancing a properly arguable fraud claim, it should not be held back unnecessarily. If a viable claim is left too long, abuse of process may still prevent it from being advanced later.
