10 setembro 2025 Alex Fawke  - Mustaqim Iqbal Dispute Resolution

Recent development of the “No Substantial Difference” Test: a view from the Court of Appeal

Over a decade has passed since the Criminal Justice and Courts Act 2015. That legislation introduced a duty on courts to withhold public law remedies (typically an order quashing a decision of a public body, or requiring it to do – or not do – something) where it appears “highly likely” that there would have been no substantial difference to the outcome for the claimant had the allegedly unlawful conduct not occurred. Until recently, there was only limited case law on the duty, particularly from appellate courts. Where courts dealt with the question of whether there was no substantial difference in outcome (i.e., the “NSD test”), it was often in the final few paragraphs of a judgment more squarely focused on the substantive public law issues. 

This has recently changed. In three judgments dealing squarely with the issue, the Court of Appeal has offered authoritative and detailed guidance on how judges should approach the NSD test. These cases are: 

This article explains the state of the law around the NSD test following these cases, and considers the key takeaways for both public authorities and claimants. 

The NSD Test

The NSD test, and the corresponding obligation on courts to refuse relief, is set out at section 31(2A), Senior Courts Act 1981 (“s. 31(2A)”). The provision was inserted by the Criminal Justice and Courts Act 2015, and was the result of a government consultation which, among other things, sought views on how to deal with the judicial review of minor defects in public decision-making which would have had no difference on the final outcome. 

Notwithstanding the limited authority from the Court of Appeal, a handful of key themes had emerged from the case law over the first decade of the duty:

  • Duty, not discretion: The courts have approached the NSD test and the duty in a robust fashion, applying what is, in practice, an ouster of their own remedial discretion. The Court of Appeal’s comments in Gathercole confirmed that the ouster would be upheld, and that a decision would not be quashed where “quashing the decision would be a waste of time and public money (because, even when adjustment was made for the error, it is highly likely that the same decision would be reached)”.[1]  It has consequently been generally accepted that judges may of their own motion decide that the duty applies and relief must be withheld, even where the defendant has not made submissions on the point.[2]
  • A lower threshold: Prior to the NSD test’s introduction, courts had a discretion to refuse remedies where it appeared essentially inevitable that the substantive outcome would have been the same.[3] It is now clear that the NSD test, while still a high bar,[4] is distinct from that discretion in two ways. First, it needs to appear “highly likely” to the court that there would have been no substantially different outcome; the threshold has been said to be “somewhere between the civil standard (the balance of probabilities) and the criminal standard (beyond reasonable doubt)”.[5] Second, the outcome need not be entirely the same, only substantially – if the outcome would have been marginally different for the claimant, the test is still met.
  • Taking care not to trespass into substantive decision-making: In R. (Plan B Earth) v Secretary of State For Transport [2020] EWCA Civ 214 (up until recently, the leading Court of Appeal judgment on the NSD test), the Court explained that s. 31(2A) had not “altered the fundamental relationship between the courts and the executive”. The judgment emphasised caution, advising that judges should not stray, “even subconsciously, into the forbidden territory of assessing the merits of a public decision under challenge by way of judicial review.”

The above aside, there was little appetite from the courts to adopt any kind of formulaic ‘test’ for when the threshold might be met. The most the courts had said on the point, prior to this year, was in the Administrative Court’s judgment in R. (Cava Bien) v Milton Keynes Council [2021] EWHC 3003 (Admin) (“Cava Bien”). In this case, the judge set out a list of 14 “key points” when considering the NSD test. The list, with reference to past cases, attempted to distil the disparate case law. The judgment included guidance on, for example, the burden of proof (which lies with the defendant), the required evidence, and relevant factors for the court. Given the limited case law on the NSD test, Cava Bien quickly became an oft-cited authority in submissions before the Administrative Court. 

Court of Appeal judgments 

In some ways departing from its earlier view that “[i]t would not be appropriate to give any exhaustive guidance on how” the NSD test applied, the Court of Appeal has recently handed down a trio of judgments which address how judges should approach the duty. We explore each case below. 

Bradbury 

Bradbury was a planning permission case, in which the claimant appealed against the Administrative Court’s decision to withhold a quashing order under s. 31(2A). While the defendant authority was found to have breached the Conservation of Habitats and Species Regulations 2017 by failing to wait for an assessment before granting permission, the court found that the outcome would not have been substantially different if the assessments had been available at the time of the decision.

The Court of Appeal dismissed the appeal, upholding the Administrative Court’s reasoning. The conditions which the authority had in fact attached to the planning permission, in order to manage the environmental implications, were identical to those which were eventually recommended in the assessments. Noting the lack of guidance from appellate courts on the NSD test, the Court of Appeal distanced itself from the Cava Bien ‘principles’. It referred to the list as “unhelpful”, and said that an attempt to apply them as a checklist was “capable of leading to error”. The judgment warned that Cava Bien should not be cited as authority for the correct approach to the NSD test and that it may not have accurately reflected the preceding case law. Instead, the appropriate approach to authorities was to refer to specific cases which may bear relevance to the present case, as this had a better prospect of assisting the court in assessing the legal and factual context.

Greenfields 

In a judgment handed down on the same day as Bradbury, the Court of Appeal allowed the claimant’s appeal in a challenge against planning permission on the substantive points, and, after considering the NSD test, decided that relief ought to be granted. This was in large part because there was insufficient evidence to establish that the highly likely threshold had been met. To withhold relief without satisfactory evidence would require the court to enter the territory of the local council defendant’s decision-making, which the Court of Appeal stated that it did not have the evidence or experience to carry out. At first instance, the judge was thus wrong to have refused permission for the judicial review on the grounds that there would not have been a substantially different outcome.

In a concurring judgment, Singh LJ provided guidance on what the duty of candour requires when public authorities seek to rely on s. 31(2A). In such circumstances, the duty of candour required the defendant itself to provide clear evidence that there would have been no substantial difference. During the Greenfields proceedings, no witness evidence was filed on the NSD point and submissions were instead presented purely by the local council’s barrister, who spoke to various documents. This approach was unacceptable, and Singh LJ said that in the future courts should “(in proper evidence, i.e. in a witness statement) be given a full accurate and clear explanation of the decision-making process used by the public authority concerned”.

Wickford 

This case concerned whether the Forestry Commissioners – the non-ministerial government department responsible for the management of publicly owned forests – were entitled to issue a restocking notice against the claimant. Restocking notices may be issued to private parties in circumstances where it appears to the Commissioners that the party has felled trees without a licence, which is a criminal offence. The claimant raised an objection to the Commissioners that, in circumstances where criminal proceedings against them have failed, it was an abuse of power to serve a restocking notice. In the judicial review proceedings, the claimant alleged that the Commissioners and the Secretary of State (via the relevant junior Minister) had unlawfully failed to consider this objection. 

The Court of Appeal accepted that the failure to engage with the objection was unlawful, but took the view that the service of the restocking notice was otherwise lawful (the relevant statutory provision did not require a criminal conviction). Interestingly, while it concluded that the Administrative Court was right to withhold relief, the Court of Appeal arrived at that conclusion without recourse to the NSD test or s. 31(2A). Lewis LJ – two months after his Greenfield judgment – explained that although the Commissioners and the junior Minister should have considered the objection, it would not have made a difference to the claimant. The specific objection raised (i.e., that the Commissioner did not have the power, or it was an abuse of power, to issue the notice) was a legal objection around the Commissioner’s jurisdiction. While the Minister was obliged to reach a conclusion on it, that conclusion would have ultimately been the subject of a judicial review claim and ruling by the courts. Either way, the claimant would have ended up in judicial review proceedings on the point. Thus, the unlawful conduct was “not material” as it did not render the final decision “unlawful, and no remedy should be granted. The NSD test and s. 31(2A) had no place in this reasoning. This reflects the point that public law remedies are always essentially discretionary and thus, even absent s, 31(2A), it is open to a court to refuse a remedy where it considers that to be a just outcome in all the circumstances.

Discussion 

These decisions provide welcome clarity on the NSD test. 

For defendants, the judgments are useful guidance on what courts will require before they are persuaded that the outcome would not have been substantially different notwithstanding the unlawful conduct. Post-Greenfields, defendants will now need to give careful thought to witness evidence that they may be able to provide to show the determinative and non-determinative factors which led to a decision. Moreover, in Wickford, public authorities now have a roadmap for an alternative argument which, under the right facts, may also be deployed either in place of, or alongside, the NSD argument. 

For claimants resisting arguments that relief should be withheld, they can expect defendants to articulate their NSD submissions early in proceedings and will have the opportunity to provide counter-arguments in good time, including in reply submissions in the event that the defendant has outlined a s. 31(2A) argument in their summary grounds for resistance. Similarly, in circumstances where defendants have not provided proper evidence, claimants will be well-positioned to argue that relief should be granted as it is likely not possible for the court to decide whether there would have been a substantial difference. While it remains the position that the court may consider the point without receiving submissions, the renewed emphasis on providing evidence pursuant to the duty of candour will favour claimants in instances where the public body has provided none.

[1]    Gathercole v Suffolk CC [2020] EWCA Civ 1179, [38].

[2]    R (Good Law Project) v Secretary of State for Health and Social Care [2021] EWHC 346, [156]-[159].

[3]    Simplex GE (Holdings) Ltd v Secretary of State for the Environment (1989) 57 P. & C.R. 306; [2017] P.T.S.R. 1041.

[4]    R. (Public and Commercial Services Union) v Minister for the Cabinet Office [2017] EWHC 1787 (Admin) per Sales LJ at [89]: "… the threshold remains a high one… ".

[5]    Glatter v NHS Herts Valleys Clinical Commissioning Group [2021] EWHC 12 (Admin), [98].