Have you found that questions of causation are becoming increasingly difficult or contentious?
Causation is often a very knotty problem in theory, can take up a lot of time in preparation, during ADR, and at trial, but tends to be quite briskly dealt with by trial judges: the medical evidence either supports it or not. Nonetheless the Claimants increasingly submit that the court should discard the comparatively simple 'but for' test in favour of a test of 'material contribution', i.e. something greater than negligible, referring to Bailey v Min of Defence 2008 EWCA 883. It is not unusual to find that the Judge agrees.
Of course it is important to bear in mind that the use of this approach is fairly narrowly confined and is in effect a practical solution to particular difficulties of proof. It must be a case where it is impossible for medical science to be able to prove one or other potential cause – see Bailey and also the contrasting decision a few months later of Hull v Sanderson. Mere difficulty in proof is not enough.
Bailey was a medical negligence case, and Hull concerned an infection allegedly caught at work. More familiar circumstances are asbestos dust claims where the injury could have been caused by a number of separate tortious events for which separate Defendants were responsible. This has been explained further in Sienkiewicz (Costello) v Greif (UK)  UKSC 10: the principle extends to cases where potential causes include environmental exposure for which there was no known or identified tortfeasor.
What about psychiatric injury? In many cases there are numerous competing potential causes of which several are likely to be not only non-tortious but from within the Claimant's own household. Psychiatric science is such that the material contribution test will often apply (as in Dickins v O2 ), but parties need to remember the need for it to be impossible to prove the claim otherwise. In Vaile v Havering  EWCA Civ 246 a teacher's psychological injury had been caused by a pupil's assault. Both the trial judge and the Court of Appeal (at the permission stage) held that the 'but for' test applied in respect of the sundry negligent acts relied upon. However, when applying this test the CA overturned the Judge's factual conclusions, and held that even though it "may be difficult for Mrs Vaile to show precisely what she or the school could have done to avoid the incident" it was likely that it would have been avoided but for the negligence complained of. Accordingly and in appropriate circumstances there is room to argue that even if the circumstances do not lead to a material contribution test, the standard of proof may be somewhat modified so that "something should have been done" will be enough. The Supreme Court has rejected the Defendant's application for permission to appeal.