## Facts

- The claimant suffered severe complications following medical treatment provided by the Ministry of Defence.
- Multiple factors contributed to the claimant’s injury, including alleged negligent post-operative care as well as pre-existing conditions and other non-negligent factors.
- The claimant contended that the defendant’s negligence materially contributed to her injuries, even though the injuries had multiple causes.

## Issues

1. Whether the defendant's material contribution to the claimant’s injury was sufficient to establish liability in circumstances involving multiple causative factors.
2. Whether the traditional "but for" test of causation is appropriate where harm arises from a combination of negligent and non-negligent factors.
3. Whether precise quantification of the defendant’s role in the causation of harm is required for liability.

## Decision

- The Court of Appeal held that a defendant may be liable if their negligence made a material contribution to the injury, even where other non-negligent factors were also causative.
- The Court found that the "but for" test is inadequate in cases involving multiple concurrent or sequential causative factors.
- The defendant’s contribution to the harm need not be the primary or dominant cause; it suffices if it is more than negligible.
- The Court confirmed that liability can be established without precise quantification of the defendant’s role, based on the overall evidence.

## Legal Principles

- Where multiple factors cause harm, liability in tort may be established if the defendant’s negligence materially contributed to the injury, not just if it was the sole or principal cause.
- The traditional "but for" test may be set aside in favour of a material contribution test in complex causation scenarios.
- Material contribution requires the defendant’s conduct to be more than negligible, but does not need to be precisely quantified.
- This approach is particularly applicable in medical negligence cases and situations with complex or multifactorial causation.

## Conclusion

Bailey v Ministry of Defence [2009] 1 WLR 1052 established that in tort law, a defendant’s material contribution to harm suffices for liability, providing a more flexible framework for causation in cases with multiple contributing factors, and particularly influencing claims in medical negligence and other complex contexts.
