This guide is maintained as a current resource for August 2026 and covers only the laws of England and Wales. Information is for general guidance, not legal advice. Consult a qualified solicitor for advice specific to your situation.
Comprehensive guide to how causation is proved in clinical negligence claims in England and Wales. Learn about the “but‑for” test, material contribution, foreseeability, key case law, expert evidence and challenges in establishing the causal link between negligent care and harm.
In clinical negligence law in England and Wales, establishing causation is a critical and often challenging part of a claim. Causation refers to the legal and factual link between a healthcare provider's breach of duty and the harm suffered by the patient. Even where it is accepted that care fell below the required standard, a claimant must still prove that this breach caused the injury or loss they experienced. This article explains how causation is proved in clinical negligence claims, including legal tests, relevant case law, evidential requirements, common difficulties, and how causation affects the outcome of claims.
Introduction
Clinical negligence claims require proof of three core elements: a duty of care owed by the healthcare provider, breach of that duty, and causation linking the breach to harm. Causation sits at the heart of negligence law because it ensures that claimants are compensated only for harm that was actually caused by substandard care, rather than for pre‑existing conditions or outcomes that would have occurred irrespective of the clinical negligence. Proving this link is essential for successful claims in tribunals and civil courts.
What Causation Means in Clinical Negligence
In legal terms, causation concerns whether the harm or loss suffered by the claimant was caused by the breach of duty. In clinical negligence law, causation has two key aspects:
- Factual causation: whether the breach actually caused the injury or loss;
- Legal causation: whether the type of injury or loss was a reasonably foreseeable consequence of the breach.
Both aspects must be satisfied for a claim to succeed. The claimant bears the burden of proof, and causation must be established on the balance of probabilities - that it is more likely than not that the breach of duty caused the harm.
The “But‑For” Test
Basic Factual Causation
The primary legal test for factual causation in clinical negligence is the “but‑for” test. This asks whether the claimant would have suffered the injury but for the healthcare provider's breach of duty. In simple terms, if the injury would not have occurred but for the negligent act or omission, causation is established.
For example, if a clinician's failure to diagnose a treatable condition led to a worsened outcome that would not have occurred with appropriate diagnosis and treatment, causation can usually be proven using this test.
Balance of Probabilities
The “but‑for” test is applied on the balance of probabilities. The court considers whether it is more than 50% likely that the breach caused the harm. If the evidence suggests that the harm would have occurred in any event, even without negligence, then causation is not established and the claim may fail.
When the But‑For Test Is Difficult to Apply
Multiple Potential Causes
Clinical negligence cases often involve complex medical situations where harm may result from a combination of factors, including the underlying disease or condition, normal risks of treatment, and negligent care. In such circumstances, it can be difficult to apply the straightforward “but‑for” test.
Material Contribution Test
Where the court cannot determine causation using the strict “but‑for” test, it may apply a material contribution approach. This test asks whether the breach of duty materially contributed to the harm - that is, whether the negligent act made a more than negligible contribution to the injury.
A key case illustrating this is Bailey v Ministry of Defence [2008] EWCA Civ 883. In that case, scientific evidence could not show that the claimant's brain injury would not have occurred but for the negligent lack of post‑operative care. However, the court found that the negligence had materially contributed to the claimant's weakened condition leading to harm, and causation was established on that basis.
Legal Causation and Foreseeability
Beyond factual causation, courts also consider whether the harm suffered was a reasonably foreseeable consequence of the breach of duty. If the type of harm was not a reasonably foreseeable outcome of the negligent act, even if factual causation is established, the claim may fail on legal causation. This principle ensures that defendants are not held liable for highly remote or unforeseeable consequences.
In clinical negligence, foreseeability typically involves medical expertise to determine whether the injury complained of was a foreseeable risk of the negligent practice or omission.
Evidential Requirements in Proving Causation
Medical Expert Evidence
Medical expert evidence is central to proving causation in clinical negligence claims. Experts explain what would have happened in the absence of negligence and whether the breach was a causative factor in the claimant's harm. Their testimony can clarify complex medical issues and help courts to apply the “but‑for” test or the material contribution approach.
Medical Records and Documentation
Detailed clinical records, test results, imaging, treatment plans, and timelines are essential to establish the factual sequence leading to harm. These documents assist legal representatives and the court in reconstructing events and assessing whether negligence caused the claimed injury.
Common Challenges in Clinical Negligence Causation
Pre‑existing Conditions
Where a claimant has an underlying medical condition, it can be difficult to show that negligent care, rather than the natural progression of disease, caused the worsened outcome. Careful expert analysis is often required to differentiate the effects.
Multiple Contributing Factors
When harm results from both negligent and non‑negligent causes, establishing that the negligent cause materially contributed to the harm remains a legal challenge. The court must assess whether the breach's contribution was significant enough to satisfy causation principles.
Speculative Claims
Claims that rely on speculation rather than substantive evidence of causation are unlikely to succeed. The court requires robust medical and factual evidence that establishes a direct or material link between negligence and harm.
Practical Considerations for Claimants
Burden of Proof
Claimants must prove causation on the balance of probabilities. This means demonstrating that it is more likely than not that negligence caused the injury. This standard guides how evidence is presented and evaluated in clinical negligence proceedings.
Timing of Evidence
Medical records and expert reports should be obtained early in the claims process. Delays can risk loss of evidence or weakened ability to reconstruct clinical events leading to harm.
Legal Representation
Specialist solicitors experienced in clinical negligence can help identify relevant evidence, instruct appropriate experts, and present causal links in a legally persuasive manner. Given the complexity of causation issues, high‑quality legal support is often critical to claim success.
Key Takeaways
Proving causation in clinical negligence cases in England and Wales involves demonstrating a direct causal link between a breach of duty and the claimant's harm. The primary method is the but‑for test, applied on the balance of probabilities. In complex cases with multiple causes, the court may use a material contribution test where the negligent act materially contributed to the harm. Both factual and legal causation must be established, supported by robust medical and expert evidence. Understanding how causation is proved helps claimants and solicitors assess the strength of clinical negligence claims and prepare evidence effectively.
