Proving causation in cancer: Court of Appeal unanimous decision

15 Feb 2016

Heneghan v Manchester Dry Docks Ltd & Others

In a successful BLM multi-defendant asbestos-related lung cancer case in which no single defendant was responsible for more than half the total exposure to asbestos, the Court of Appeal has today unanimously approved a new approach to proof of causation, and has held that damages should be apportioned in line with the individual defendant’s relative share of exposure. Heneghan establishes the correct approach to causation and divisibility of damages in such cases, and has a significant effect on other occupational cancer claims.


The deceased died from lung cancer in January 2013. He had been exposed to asbestos by ten employers. Of these, six were the defendants in this case. The deceased worked for the six defendants between 1961 and 1974.

The deceased’s total asbestos exposure was 133 fibre/ml years. Of this, the defendants were responsible for 46.9 fibre/ml years, or 35.2%. Amongst the defendants, the single largest contribution was 10.1%; the smallest was 2.5%.

Judgment was entered by consent against all the defendants. The issue was whether each defendant was liable in full on the basis that each had materially contributed to the cancer, as the claimant argued, or only for its proportionate share. If the claimant was correct, damages were £175,000. If the defendants were correct, damages were £61,600 (35.2%).

At first instance, Jay J held that apportionment was the correct outcome. He awarded damages against each defendant in proportion to the increase in the risk of lung cancer for which it was responsible, ie. in proportion to its share of exposure.

The claimant appealed.

Court of Appeal
Causation: two stages

Lord Dyson MR accepted that, as Jay J found, there must be a two-stage approach to causation here.

(i) The first stage was “what” caused the deceased’s lung cancer;
(ii) The second stage was “who” caused the lung cancer.

The answer to the “what” question here was “asbestos”. Epidemiology showed that on the balance of probabilities asbestos was a cause of the deceased’s lung cancer. The relative risk of the cancer having been caused by asbestos (as opposed to other potential causes such as smoking) was greater than 2:1; i.e. the risk was doubled.

The “who” question arises in a multi-defendant case. Medical science cannot determine which defendant’s asbestos caused the cancer. It could not be proved that any individual defendant had doubled the risk that the deceased would develop lung cancer.

Claimant’s submissions

The claimant argued that the court should infer that each source of asbestos contributing to the total exposure materially contributed to the disease. For the claimant:

(i) The deceased’s lung cancer was caused by asbestos;
(ii) The causal connection between the cancer and the asbestos was established by reason of the cumulative dose;
(iii) The asbestos acted in multiple ways to promote carcinogenesis;
(iv) Asbestos from each defendant was likely to have been inhaled and distributed in the lungs in a similar way;
(v) Asbestos fibres from each source were likely to have played a part in the carcinogenic process; and
(vi) Each defendant therefore materially contributed to the cancer (so each was liable in full).


Lord Dyson accepted points (i), (ii) and (iii); he rejected (iv), (v) and (vi).

Proof of causation

Lord Dyson MR explained the three methods of proving causation in disease cases:

(i) The ‘but for’ test – but for the defendant’s negligence, the claimant would not have suffered the disease;
(ii) The material contribution test - per Bonnington Castings v Wardlaw [1956] AC 613 - where the disease is caused by cumulative exposure, the defendant’s liability is based on making a material contribution to the disease; and
(iii) The Fairchild exception – causation is proved on the basis of the defendant having materially increased the risk of the disease.

The claimant could not satisfy the ‘but for’ test. For example, even if the deceased had not been employed by the defendant responsible for 2.5% of the asbestos exposure, he would still probably have developed lung cancer. There was no specific evidence of individual causation as against the defendants.

The claimant’s medical expert (Dr Rudd) accepted that the current understanding of the biological mechanisms did not form the basis for attribution and apportionment of the causation of particular cancers. The process is random. One cannot say that “this employer contributed to this fibre which had that effect on that cell.”

Lord Dyson MR approved Swift J’s rejection of the material contribution/Bonnington test in relation to lung cancer in Phurnacite [2012] EWHC 2936. Swift J in Phurnacite stated that in respect of a claimant’s cancer, the occupational exposure to a carcinogenic agent might or might not have contributed to it. This was very different from Bonnington, where the defendant’s exposure had a cumulative effect. Lord Dyson MR agreed with Jay J that material contribution did not apply here.

Jay J was right to reject Dr Rudd’s view that every period of exposure contributed to development of the cancer. The epidemiological evidence did not justify this – it only allowed quantification of the risk.

Lord Dyson MR explained that the claimant’s reliance on the material contribution test/Bonnington ignored the fundamental difference between making a material contribution to an injury, and materially increasing the risk of an injury. As Lord Hoffmann said in Barker v Corus [2006] 2 AC 572, if the basis of liability is the wrongful creation of a risk or chance of causing the disease, the damage which the defendant should be regarded as having caused is the creation of such a risk or chance.


Causation could not be established against any of the defendants under the ‘but for’ test. It was not possible to infer from the epidemiological evidence that any of the defendants made a material contribution to the deceased’s lung cancer. But all of the defendants materially contributed to the risk that he would develop lung cancer.

Lord Dyson MR considered that the material contribution test/Bonnington applies where the court is satisfied on the scientific evidence that the defendant’s exposure has in fact contributed to the injury. Where the scientific evidence does not permit a finding that the exposure attributable to a particular defendant contributed to the injury, the law’s response is to apply the Fairchild exception. It could not be said here on the basis of medical science which (if any) of the defendants were responsible for the exposure which caused the cell changes which initiated the genetic changes culminating in the cancer. Therefore Fairchild applied to the second stage here. [Because Fairchild applies, the apportionment rules in Barker must apply, so damages were apportioned in line with contribution to the increase in risk.] The Court of Appeal dismissed the claimant’s appeal.


The Court of Appeal in Heneghan has accepted a new approach to causation and damages in multi-defendant asbestos-related lung cancer cases. The Court of Appeal endorsed the two-stage test. For the claimant to succeed, the cancer must be shown to be attributable to asbestos on the basis of epidemiological evidence. The relative risk of the cancer having been caused by asbestos must be greater than 2:1. Asbestos must have doubled the risk. Where the claimant can satisfy this first stage (the “what” question), the second stage applies – the “who question”. If the ‘but for’ test was applied to the individual defendants in Heneghan, the claimant would have recovered nothing.

Material contribution/Bonnington cannot apply because medical science cannot show which defendant’s asbestos (if any) contributed to the disease. Epidemiology cannot be stretched to show more than risk. As Swift J said in Phurnacite, the occupational exposure might or might not have contributed.

A just approach was advocated by the defendants in Heneghan. This approach successfully rebutted the claimant’s argument that each defendant should be liable in full.

Because we can medically attribute the lung cancer to asbestos, and we know that each defendant’s breach of duty has contributed to the risk of that lung cancer developing, liability can only be based on Fairchild. But (because section 3 of the Compensation Act 2006 applies to mesothelioma only) Barker and apportionment of damages also applies. So even though the disease is indivisible, damages are divisible. Each defendant pays damages in proportion to its contribution to the risk/share of exposure. The two alternatives to this – either the claimant receives nothing or a defendant responsible for a tiny contribution to risk (eg. 2.5% of exposure) is required to pay 100% of damages, are both highly unattractive.

Should there be different approach where a defendant is responsible for more than 51% exposure?

At first instance, Jay J said obiter that in respect of a tortfeasor responsible for 56% of the deceased's overall exposure, he would have had no difficulty in finding such a defendant liable in full on the balance of probabilities. Lord Dyson MR chose not to address this question. The defendants consider that Jay J's obiter comment cannot be correct. There are three main reasons for this:

(i) Acceptance of the two-stage test illustrates the difference between the "what" question and the "who" question. Medical attribution to asbestos is not the same as legal responsibility. Even if one defendant is responsible for 90% of exposure, it cannot be said that but for this exposure the defendant would not have developed lung cancer. The mechanism of causation is "inscrutable". All that can be said is that asbestos is more likely than not to be involved in the process of causation - not that any particular defendant's asbestos was the cause. It cannot be correct to impose 100% liability on a defendant whose fault might have been wholly uninvolved.
(ii) Lord Dyson MR accepted that each defendant's asbestos contributed to risk. So per Fairchild and Barker, a defendant's liability is for its contribution to risk - a 56% contribution to risk results in liability for 56% of the damage - because the damage for which the defendant is responsible is contribution to risk. This is what Fairchild and Barker established.
(iii) It cannot be right that the correct test of causation varies depending on the particular circumstances of the case. One cannot say that the but for test applies with one defendant, but Fairchild/Barker applies when there is more than one defendant. The application of Fairchild is predicated on the idea that we cannot say which exposure to asbestos caused the cancer. The but for test translated into its statistical expression as the doubling the risk test makes sense when faced with a choice between two separate causes: ie. between smoking and a tortious agent. It does not make sense to perform the exercise twice when (a) choosing between a non-tortious agent and a tortious agent, and then (b) going on to choose between two or more tortious agents. Looking at the analysis in this way, we can see that 56% of the asbestos exposure is not actually 56% of the risk - it is less than this this, because it does not take account of the exercise at (a), above.

Nick Pargeter

Malcolm Keen

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Disclaimer: This document does not present a complete or comprehensive statement of the law, nor does it constitute legal advice. It is intended only to highlight issues that may be of interest to clients of BLM. Specialist legal advice should always be sought in any particular case.

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