Pushing the Boundaries of Causation in Disease Claims: Mather v Ministry of Defence [2021] EWHC 811 (QB)

Earlier this year, the High Court decided not to exercise its general powers of case management and order a trial of preliminary issue, pursuant to CPR 3.1(2)(i), in Mather v Ministry of Defence [2021] EWHC 811 (QB).

The case in question is an occupational disease action, commenced by a former RAF painter and finisher. He is seeking damages for multiple sclerosis (MS) and psychiatric injury, allegedly caused by workplace exposure to organic solvents (the exogenous factor), from 1989 to 2003. It is argued that the defendant was negligent and breached its duty of care under the Control of Substances Hazardous to Health (COSHH) Regulations.

Central to a determination on liability, the court will have to first be persuaded that the claimant’s exposure could have caused his MS (generic causation), and second, that it did cause his MS (individual causation).

Such was the defendant’s confidence in its causation defence that it sought a trial of preliminary issue, either by:

‘(a) defining a preliminary issue on causation with the Claimant's best case on exposure being the assumed facts, and limiting oral evidence to medical causation; or

(b) formally opening the trial, limiting oral evidence to that relevant to medical causation, and then making a ruling on causation, with other issues to follow if necessary’.

Indeed, the defendant believed that if it were to succeed on causation alone, it would render the trial of remaining issues (including breach of duty, limitation and quantum) ‘otiose’ and therefore save on expenditure of time and costs.

However, having regard to the overriding objective, whose purpose is to ensure that litigation is dealt with both ‘expeditiously’ and ‘fairly’, Mr. Justice Freedman decided that it would not be ‘just or prudent’ to order a trial of preliminary issue on either basis [(a) or (b)].

It was considered possible that granting the order could in fact result in substantial increases in costs and delays. With many of the ‘assumed facts’ (the defendant’s condensed version of the claimant occupational hygienist’s evidence) objected to, it was foreseen that there could be multiple appeals (especially if issues of breach and causation were to overlap) and duplication of witnesses (with the capacity to contradict themselves when recalled).

Full text judgment can be accessed here.

The trial is currently expected to go ahead in 2022. Ms. Willmott, of the Government Legal Department, has acknowledged that Mather is likely to capture wide ‘public interest and significance’:

‘It has the potential to become a leading precedent on causation in the law and could open the way for other sufferers with MS to argue that their own conditions were “caused” by similar environmental exposures’.

Aspects of breach of duty, interwoven with causation, to be tested at the trial of liability, will likely comprise of:

  • Whether solvent exposure after 1994 can be ignored as irrelevant if levels were below workplace threshold limits prescribed by the Regulations? This calls into question several issues: (1) whether threshold limits can be determinative, if cumulative (total) exposure is relevant to the development of MS; and (2) whether, as a question of law, the defendant has a duty to reduce exposure below recognised standards (permitted levels will be outlined by occupational hygiene expert, Professor Cherrie), or to the lowest level reasonably practicable; and
  • Whether continued solvent exposure post-2000 (the year the claimant was diagnosed with MS) affected the progress or acceleration of the disease and its symptoms, i.e. whether this period of exposure was causative or contributory. Which party bears the onus of proof? The claimant argues that absence of scientific evidence could indicate a causative relationship, whilst the defendant contends that without scientific evidence, no correlative relationship can be said to exist.

On the issue of causation specifically, the Court will hopefully address the following:

  • Whether MS is a divisible or indivisible condition. The defendant's case is that it is indivisible, but the claimant refers to conflict between Bonnington Castings Ltd v Wardlaw [1956] UKHL 1 and Williams v Bermuda[2016] UKPC 4, on pneumoconiosis. It is therefore submitted that there is scope for uncertainty over what constitutes an (in)divisible condition;
  • If indivisible, whether the ‘material contribution’ test is appropriate. Stringent reading of the 3 categories defined in Heneghan v Manchester Dry Docks [2016] EWCA Civ 86 and also Ministry of Defence v AB & Ors [2010] EWCA Civ 1317 would suggest that the test is only fit for divisible diseases, but the claimant points to Williams as providing room for application;
  • If indivisible, whether the ‘material increase in risk’ test is suitable. This would involve an extension of the Fairchild v Glenhaven Funeral Services Ltd[2002] UKHL 22 exception, beyond exclusively mesothelioma or lung cancer cases;
  • If indivisible, but there is judicial reluctance to extend the Fairchild exception and the ‘material contribution’ test is incompatible, whether causation is to be decided on the basis that the claimant would not have suffered the disease ‘but for’ the defendant’s negligence;
  • Whether the claimant’s psychiatric injury is to be characterised as divisible, even if their MS is indivisible. Generally, psychiatric injury has been treated as a divisible condition. However, if the psychiatric injury is a consequence of the MS, is it possible to treat the psychiatric injury as anything other than the designation of the MS, i.e. also indivisible?; and
  • Whether the claimant is required to prove a more than doubling of risk, in the context of contracting the index condition, with MS being a disease generally seen to have an unknown aetiology. This is not the case for, e.g. mesothelioma [Sienkiewicz v Greif [2011] UKSC 10], palmar arch disease [Transco v Griggs[2003] EWCA Civ 564], dermatitis [McGhee v National Coal Board [1972] UKHL 7], etc. This was also not the case for a former MoD employee, who was exposed to organic solvents and subsequently developed Parkinson’s disease – see Wood v Ministry of Defence [2011] EWCA Civ 792.

Readers can expect a comprehensive summary of the trial judge’s ruling once it is handed down, potentially in the new year. Legal professionals are anticipating some ‘fascinating arguments’ and are adamant that the case could end up reaching the Supreme Court.[i]


[i] Thomas Herbert, ‘High Court Refuses Defendant's Request to Try Causation as a Preliminary Issue in Claim under the COSHH Regulations’ (9 April 2021 Ropewalk Chambers) <https://www.ropewalk.co.uk/knowledge-sharing/blog/disease/1800/high-court-refuses-defendants-request-to-try-causation-as-a-preliminary-issue-in-claim-under-the-coshh-regulations> accessed 19 August 2021.