Proving Causation in Personal Injury Claims

In personal injury law in England and Wales, proving causation is a pivotal legal step. Even where a claimant can show another party owed a duty of care and breached that duty through negligence or a breach of statutory obligation, a claim will fail unless it also establishes that the defendant's conduct actually caused the claimant's injury or loss. Causation addresses the legal and factual link between an incident and the harm suffered, and it is essential for securing compensation in claims involving road traffic accidents, workplace injuries, slips and falls, clinical negligence and other types of personal injury.

This article explains what causation means in law, the legal tests used to prove it, how evidence supports causation in claims, common challenges and practical steps for claimants and solicitors.

What Is Causation?

Causation in personal injury law refers to the requirement to show a direct link between the defendant's breach of duty and the claimant's injury or loss. It is the third element of negligence after duty of care and breach, and must be demonstrated on the balance of probabilities - meaning it is more likely than not that the defendant's conduct caused the harm.

Causation has two distinct aspects in English tort law:

1. Factual causation – whether the defendant's conduct was the factual cause of the injury, typically tested by the “but for” test.
2. Legal causation – whether the injury was a reasonably foreseeable consequence of the breach, sometimes described as avoiding too remote harm.

Both aspects are required before compensation can be awarded.

Factual Causation: The “But For” Test

The primary test for factual causation asks a simple question:

“Would the claimant's injury have occurred but for the defendant's negligent act or omission?”

If the injury would not have occurred without the defendant's conduct, factual causation is established. In straightforward accidents, such as a pedestrian struck by a driver who ran a red light, the link between negligent driving and injury is clear under this test.

However, complications arise where multiple factors could have caused the injury or where pre‑existing conditions are involved. In such cases, alternative legal tests may be applied.

Legal Causation: Remoteness and Foreseeability

Even if factual causation is established, a claimant must also show that the type and extent of harm were reasonably foreseeable at the time of the breach. This ensures that defendants are not held liable for consequences too remote from their actions. For example, in rare circumstances, injury from a seemingly unrelated event might be considered too distant from the original negligent act to attract legal liability.

Judicial authority such as Smith v Leech Brain & Co Ltd illustrates that once causation is proven, a defendant can be liable for the full extent of injury even where the claimant was unusually susceptible to harm (the eggshell skull rule).

Material Contribution and Multiple Causes

In cases where more than one factor could have caused the injury, the traditional but for test may be difficult or impossible to apply. English courts have recognised that where a breach of duty by the defendant materially contributed to the risk of harm, causation can sometimes be established even if the defendant's conduct was not the sole cause. This approach has its roots in authorities such as Bonnington Castings Ltd v Wardlaw (dust exposure case) and McGhee v National Coal Board, where material contribution sufficed to establish factual causation.

These principles are particularly relevant in cases involving industrial disease, gradual exposure injuries or overlapping exposures. However, courts apply these extended tests carefully, generally requiring evidence that the defendant's breach more than minimally contributed to the harm.

Evidence Supporting Causation

Medical Records and Expert Reports

Medical evidence is critical for linking an accident to the claimant's injuries. Expert medical testimony explains:

• The diagnosis of injuries;
• The likely cause and progression of the injury;
• Whether the injury would have occurred without the defendant's breach.

In complex cases involving pre‑existing conditions or multiple potential causes, expert opinions help the court assess whether the defendant's conduct more likely than not caused the injury.

Accident Reports and Scene Evidence

Police collision reports, workplace accident records, CCTV footage and site photographs can help establish the sequence of events and how the defendant's conduct led to the claimant's harm. This type of evidence supports both factual and legal causation by contextualising the incident.

Witness Statements

Eyewitness accounts contribute to the narrative of what happened, help clarify cause‑and‑effect relationships at the time of the incident, and can corroborate documentary and medical evidence.

Special Considerations in Clinical and Complex Cases

Clinical Negligence

In clinical negligence claims, proving causation may involve medical experts demonstrating that a negligent treatment or misdiagnosis caused an identifiable worsening of the claimant's condition. The but for test is still central, but where multiple factors might influence outcome, evidence must show a material contribution by the negligent act.

Intervening Events

If an intervening event (novus actus interveniens) occurs after the defendant's breach and independently causes harm, the chain of causation may be broken. Determining whether the intervening event was sufficiently independent to absolve the original wrongdoer is a question of fact and law, often requiring expert analysis.

Common Challenges in Proving Causation

Pre‑Existing Conditions

When a claimant has a prior condition exacerbated by the defendant's actions, establishing that the accident significantly worsened the condition (rather than unrelated progression) is essential. Expert medical analysis plays a key role in these scenarios.

Multiple Potential Causes

Where there are several plausible causes for an injury, proving that the defendant's breach was the more probable cause can be challenging. Material contribution principles and judicial interpretation of case law guide the analysis in such contexts.

Practical Steps for Claimants

1. Seek Prompt Medical Attention
Early medical records establish a contemporaneous link between the accident and injuries, strengthening causation arguments.

2. Gather Comprehensive Evidence
Collect photographic, documentary and witness evidence of the accident scene, incident details and any contributing factors.

3. Obtain Expert Reports
Engage medical and other experts early to analyse causation issues and articulate the link between breach and harm in technical reports.

4. Work with a Specialist Solicitor
Experienced personal injury solicitors ensure causation issues are addressed effectively, including preparing evidence that satisfies the balance of probabilities standard.

Key Takeaways

Proving causation in personal injury claims in England and Wales requires establishing both factual causation - typically through the “but for” test - and legal causation - showing that the harm was a foreseeable consequence of the defendant's breach of duty. In complex circumstances, courts may apply material contribution principles where multiple causes exist. Strong medical documentation, expert analysis, accident evidence and witness statements all support effective causation arguments. Claimants must demonstrate on the balance of probabilities that the defendant's conduct was a real and substantial cause of their injury to secure compensation.

James William Steven Parker

James is the founder of UKLegalGuides.com and a former agent at the Ministry of Justice (UK). With a background in processing legal claims, he launched this platform to make the laws of England and Wales accessible to everyone.