Challenging HMRC Decisions by Judicial Review in 2026

Judicial review is one of the most powerful legal tools available to a taxpayer facing an unlawful, irrational, or procedurally unfair decision by HMRC. Where the ordinary statutory appeal process cannot adequately address the wrong that has been done, or where HMRC has acted outside its legal powers entirely, an application for judicial review before the Administrative Court can compel HMRC to reconsider, set aside its decision, or compensate for the consequences of its unlawful conduct. In 2026, as HMRC continues to expand its investigative and enforcement reach, understanding when and how to bring a judicial review challenge has never been more important for businesses and individuals in dispute with the tax authority.

What Is Judicial Review and Why Does It Apply to HMRC?

Judicial review is the process by which the High Court supervises the exercise of public power. Because HMRC is a public body exercising statutory functions, its decisions are subject to judicial scrutiny in a way that purely private commercial decisions are not. When HMRC makes a decision that is unlawful, whether because it has exceeded its legal authority, applied the wrong legal test, acted in a procedurally unfair manner, or behaved in a way that no reasonable public authority could behave, the Administrative Court has jurisdiction to intervene. A successful judicial review application against HMRC can result in the quashing of the decision under challenge, a mandatory order requiring HMRC to act in a particular way, or a declaration that HMRC has acted unlawfully.

It is important to understand that judicial review is not an appeal on the merits of a tax liability. The Administrative Court does not substitute its own view of how much tax is owed. Rather, it examines the legality of the process by which HMRC reached its decision and, where that process is found to be defective, sends the matter back to HMRC to be reconsidered lawfully. This distinction is critical because it defines both when judicial review is appropriate and what outcome a claimant can realistically expect.

When Is Judicial Review the Right Route to Challenge an HMRC Decision?

The first question any adviser must ask is whether the taxpayer has an adequate alternative remedy. The courts have consistently held that judicial review should not be used as a substitute for a statutory appeal where such an appeal is available and provides an effective remedy. A taxpayer who disagrees with a VAT assessment, for example, would ordinarily be expected to pursue an HMRC internal review and then a formal appeal to the First-tier Tribunal before seeking judicial review. The court will refuse permission for judicial review if a suitable alternative remedy exists and has not been exhausted.

However, there are numerous circumstances in which judicial review is either the only available route or clearly the more appropriate one. This is the case, firstly, where there is no statutory right of appeal against the particular decision HMRC has taken. Secondly, it applies where HMRC has acted in a manner that goes beyond a mere error on the merits, raising a genuine public law defect that the tribunal cannot remedy. Thirdly, judicial review may be the right route where HMRC’s conduct is so procedurally improper that waiting for the tribunal process to run its course would itself cause irreparable harm to the claimant. In each of these scenarios, specialist legal representation is essential from the outset.

The Legal Grounds on Which HMRC Decisions Can Be Challenged

The grounds on which a judicial review challenge against HMRC may be mounted were classically formulated by the House of Lords in Council of Civil Service Unions v Minister for the Civil Service [1985] AC 374, and they remain the framework courts apply today. The three core grounds are illegality, irrationality, and procedural impropriety, though the courts have developed these over the decades to encompass proportionality, legitimate expectation, and breaches of common law fairness.

Illegality means that HMRC has acted outside its legal powers, either by doing something it has no statutory authority to do or by misunderstanding the legal limits of a power it does possess. If HMRC purports to exercise a discretion it does not have, or applies a legal test that is simply wrong, its decision will be unlawful on grounds of illegality. Taxpayers facing HMRC investigations that involve demands for information beyond the scope of HMRC’s statutory powers, for example, may have a strong illegality ground.

Irrationality, often described by reference to the classic statement in Associated Provincial Picture Houses Ltd v Wednesbury Corporation [1948] 1 KB 223, means that HMRC’s decision is so unreasonable that no reasonable public authority, properly directing itself, could have made it. This is a high threshold, but it is regularly reached in practice where HMRC has ignored highly relevant evidence, taken into account wholly irrelevant factors, or reached a conclusion that is simply irrational on the material before it. Where HMRC penalties are assessed in circumstances where the facts clearly did not justify the level of sanction imposed, an irrationality challenge may be available alongside or instead of the ordinary penalty appeal route.

Procedural impropriety covers a broad range of failures by HMRC to follow fair process. This includes failing to give the taxpayer a fair opportunity to respond before a decision is made, failing to consult where consultation was required, failing to give adequate reasons for a decision, and breaching HMRC’s own published policies and guidance in a way that causes prejudice to the taxpayer. The duty to act fairly is a fundamental principle of public law, and HMRC is not exempt from it.

Legitimate Expectation as a Ground for Judicial Review Against HMRC

One of the most frequently litigated grounds in judicial review cases involving HMRC is legitimate expectation. The principle, established in domestic law through cases including R v Inland Revenue Commissioners, ex parte MFK Underwriting Agencies Limited [1990] 1 WLR 1545, is that where HMRC has made a clear, unambiguous, and unqualified representation to a taxpayer as to how it will treat a particular matter, and the taxpayer has relied on that representation in ordering their affairs, HMRC may be prevented from departing from that representation without giving the taxpayer an opportunity to be heard and, in appropriate cases, without being held to it entirely.

In practice, legitimate expectation arguments arise in contexts including HMRC clearance decisions that are subsequently reversed, published concessions that are withdrawn without adequate notice, and individual rulings given to a taxpayer that HMRC later seeks to resile from. The Court of Appeal’s decision in David Beadle v HMRC [2020] EWCA Civ 562 confirmed that legitimate expectation arguments can in principle be raised in enforcement proceedings, although the extent to which the First-tier Tribunal can entertain such arguments as part of a statutory appeal remains a contested and developing area of law. Where there is any doubt about the appropriate forum, a taxpayer facing a significant legitimate expectation issue should take an early case assessment from specialist solicitors before committing to a particular route.

The Procedural Requirements for Bringing a Judicial Review Claim Against HMRC

Judicial review claims are governed by Part 54 of the Civil Procedure Rules. A claim must be filed promptly and in any event within three months of the date of the decision being challenged. This time limit is strictly applied, and the courts will only extend it in exceptional circumstances. In some contexts, including certain planning and procurement decisions, even shorter time limits apply, and while tax cases do not generally attract these shorter periods, the three-month window can pass quickly, particularly where a taxpayer is attempting to resolve the matter informally or is waiting for HMRC to respond to a pre-action letter.

Before filing a claim, a claimant must send HMRC a pre-action protocol letter setting out the decision being challenged, the grounds of challenge, and the remedy sought. HMRC then has 14 days to respond, though in practice extensions are frequently agreed. This pre-action stage is important and should not be treated as a formality: a well-drafted pre-action letter from experienced tax investigation solicitors will frequently prompt HMRC to reconsider its position without the need for full litigation, saving time and cost for both parties.

If the matter proceeds to court, the claimant must first obtain permission from a judge to bring the claim. The permission stage is a filter designed to weed out claims that are unarguable or hopeless, and while it is not an insurmountable hurdle for a well-founded claim, it underscores the importance of careful preparation. A claimant who rushes to judicial review without properly identifying their grounds, gathering supporting evidence, and exhausting any available alternative remedies is likely to find their application refused at the permission stage.

Key Decisions in 2025 and 2026 Shaping Judicial Review Against HMRC

The courts have continued to develop the law on judicial review of HMRC decisions in recent years. The Supreme Court’s decision in R (Haworth) v HMRC [2021] UKSC 25 remains highly significant for taxpayers challenging follower notices, having confirmed that HMRC’s decision to issue such a notice is amenable to judicial review and that the court will scrutinise whether HMRC had reasonable grounds for concluding that a judicial ruling was relevant to the taxpayer’s arrangements. The decision sent a clear signal that HMRC’s exercise of its more aggressive statutory powers is not beyond judicial scrutiny, and that taxpayers who receive notices they consider to be ill-founded have a real prospect of success in challenging them before the Administrative Court.

In parallel, the expanding scope of HMRC’s enforcement action against businesses, including the increased use of statutory demands and the presentation of winding-up petitions where the underlying liability is disputed, has created new pressure points at which judicial review arguments intersect with insolvency law. Where HMRC presents a winding-up petition based on a debt that is genuinely disputed on substantial grounds, there is a well-established jurisdiction in the Companies Court to restrain that petition as an abuse of process. In more serious cases, where the petition itself reflects a decision made without lawful authority or in breach of a legitimate expectation, the Administrative Court’s judicial review jurisdiction may provide an additional or alternative remedy.

What a Successful Judicial Review of an HMRC Decision Can Achieve

When a judicial review claim succeeds, the court has a range of remedies available. A quashing order sets aside the decision under challenge, treating it as if it never existed. A mandatory order compels HMRC to take a particular step, such as providing reasons for a decision it had unlawfully failed to explain. A prohibiting order prevents HMRC from taking a step it has threatened to take unlawfully. A declaration confirms that HMRC has acted unlawfully without necessarily setting aside any particular decision. In appropriate cases, damages may also be available, though this is relatively uncommon in a pure public law context.

It is important to be realistic about what judicial review achieves. Quashing an HMRC decision does not extinguish the underlying tax liability: it sends the matter back to HMRC to be decided again, this time lawfully. However, this can be enormously valuable in practice, because a properly conducted reconsideration frequently results in a significantly different and more favourable outcome for the taxpayer, particularly where the original decision was tainted by procedural unfairness or a failure to consider relevant evidence. Working with experienced HMRC appeal lawyers throughout this process is critical to ensuring the reconsideration is properly managed.

How LEXLAW Can Help You Challenge an Unlawful HMRC Decision

At LEXLAW our dual-qualified solicitors and barristers have extensive experience in bringing and defending judicial review applications against HMRC across a wide range of tax contexts. We advise on the full spectrum of public law challenges to HMRC conduct, from the initial assessment of whether grounds exist, through the pre-action protocol stage, to permission hearings and substantive hearings before the Administrative Court. We also advise on the interaction between judicial review and the statutory appeal process, ensuring that our clients pursue the right route at the right time and do not inadvertently compromise either avenue by acting without specialist guidance.

If you have received an HMRC decision that you believe is unlawful, procedurally unfair, or contrary to a clear representation previously made to you, we urge you to seek advice without delay. The three-month time limit for judicial review claims moves quickly, and delay in taking legal advice is one of the most common reasons why otherwise strong claims are lost before they begin. Contact our team today for a confidential, fixed-fee case assessment and let us advise you on whether judicial review is the right tool for your circumstances.