1. Bailey-v-MOD  1 WLR 1052,  EWCA Civ 1012 was a brain damage case. There was a single indivisible injury. There were cumulative causes. The negligent cause made a material contribution to the injury. Waller LJ held:
“I would summarise the position in relation to cumulative cause cases as follows. If the evidence demonstrates on a balance of probabilities that the injury would have occurred as a result of the non-tortious cause or causes in any event, the claimant will have failed to establish that the tortious cause contributed. Hotson exemplifies such a situation. If the evidence demonstrates that 'but for' the contribution of the tortious cause the injury would probably not have occurred, the claimant will (obviously) have discharged the burden. In a case where medical science cannot establish the probability that 'but for' an act of negligence the injury would not have happened but can establish that the contribution of the negligent cause was more than negligible, the 'but for' test is modified, and the claimant will succeed.”
2. So, there are two questions to be asked before the question of material contribution arises. Further, medical science has to be able to establish that the negligent event made a material contribution. The case clearly concerned causation of a single injury.
3. Bailey has been applied in Canning-Kishver-v-Sandwell & West Birmingham Hospitals NHS Trust  EWHC 2384 QB and Popple—Birmingham Women’s NHS Foundation Trust  EWCA Civ 1628 Ward J at . The latter case was an obstetric injury case involving the well known “ten minute” rule beyond which acute profound asphyxia will be damaging to the child. There was uncertainty as to whether the period of APA was 15 or 20 minutes in the particular case. If 20 minutes then there was a negligent and non-negligent contribution to the period of damaging hypoxia. Ward LJ held that “If it did take 20 minutes, the damage done in the last five minutes must have made a contribution to the overall harm which was more than minimal. I cannot see why the Bailey principle does not apply.”
4. In Dickins-v-O2 plc  EWCA Civ 1144 Smith LJ, giving the lead judgment, questioned whether the trial judge had been right to apportion a psychiatric injury by reference to contributions from its negligent and non-negligent causes. The parties had not taken the point on appeal, but Smith LJ noted Bailey-v-MOD and observed that apportionment is only appropriate where the injury is divisible or where the negligence has exacerbated and existing injury or condition, which she thought might not be the case with a psychiatric injury. The implication is that Bailey may not be applicable in relation to divisible injuries or where the negligent event has aggravated an existing injury. In those cases the material contribution has to be quantified so as to identify the injury attributable to the negligent cause.
5. There may be some cases where the Court will face difficulty in identifying whether an injury is divisible or indivisible. For example, in brain injury cases the severity of the injury may well be related to the period over which the claimant suffered hypoxia, or, following a brain tumour or injury, raised intracranial pressure. Some of that period may be caused negligently, some non-negligently. Does the difficulty of quantifying the exacerbation or contribution made by the negligent injury thereby identify the injury as indivisible? Is a Claimant better off if the experts say that they cannot quantify the exacerbation than if the experts make a guesstimate of, say 20%?
6. In some cases, therefore, the evidence may show that the injury would have been less severe had the negligence not occurred, but the evidence cannot show how much less severe, only that the negligence has made a material contribution to the final outcome.
7. In the recent case of Reaney-v-University of North Staffordshire NHS Trust  EWHC Civ 3016, the claimant had a pre-existing severe spinal injury but suffered pressure sores due to clinical negligent. The judge found that she had significantly increased care needs as a result. Interestingly however he said that even if he had found that the defendant’s negligence had materially contributed to the need for significant professional care, then following Bailey, the claimant would have recovered damages for such care in full:
“In my judgment, on the evidence, the Defendants' negligence has made the
Claimant's position materially and significantly worse than it would have been but
for that negligence. She would not have required the significant care package
(and the accommodation consequent upon it) that she now requires but for the
negligence. Had I had any doubts in this case about the issue of causation in the
"but for" sense, I would have been inclined to find that the Defendants had
"materially contributed" to the condition that has led to the need for the 24/7 care
of the nature discussed earlier in this judgment and that the lack of any joint or
concurrent tortfeasor as a potential direct compensator (and/or from whom a
contribution might be sought by the Defendants) is no answer to a full claim
against the Defendants: cf. Bailey v Ministry of Defence. However, as I have
indicated, I consider that causation is established by what might be termed the
more conventional route.”  Foskett J.