A meeting of minds

The use of forensic evidence in criminal trials and medical specialists in personal injury cases are probably the best known examples of legal use of expert testimony. However, environmental legislation defines the areas of regulatory responsibility more and more, with the result that such legislation also defines areas of liability and answerability in law. The legal provisions may also include inquiry processes to examine current practice or new proposals.

The provisions of various legal frameworks in the international arena differ in detail rather than intent and common themes emerge from the use of expert testimony.

Legal cases and public inquiries in Ireland, an inquiry in Belgium, the Netherlands' Press Complaints Commission equivalent, UK Select Committees, all have common elements although they differ in their ability to accommodate expert testimony.

Environmental issues can be highly complex. The facts of a case which involve large scale pollution, violation of licence and permit conditions or ill-advised development of a contaminated site are likely to hinge upon highly technical elements. This is where the expert witness is likely to be called in. It has been said, somewhat cynically, that if 20 different experts are made to sit around a table, then 20 sets of opinions on the same subject will emerge. This may appear flippant but it is based on the fact that 'cut and dried' environmental issues are the exception rather than the rule.

This sits uneasily with a process intended to establish facts via either an adversarial or inquisitorial examination of evidence. The sartorial fraud perpetrated on the emperor in the fable would be easily addressed through criminal proceedings, being a simple crime which can be readily defined under the existing legislative framework.

But, compare this with a situation where the emperor's new clothes – if they did exist in physical form – disintegrate after falling into the local river. An analysis of the water shows high levels of chemical X which can be traced to a factory upstream and which is known to attack textiles.

The scene is now set for a damages case with a proliferation of expert testimony. Experts will need to testify that the sample of river water was taken and analysed correctly. Other experts must testify to the corrosive properties of chemical X on textiles and confirm that the levels present in the river water were capable of causing the damage. The clothes manufacturers would probably have to defend themselves in relation to the quality of their product.

The users of chemical X, in turn, would try to defend themselves against allegations of negligence and of having polluted the river.

The scenario now begins to take on nightmare dimensions. The analytical expert reveals under examination that the levels of chemical X determined by analysis are subject to uncertainty. This is quite normal in analytical chemistry but is not a fact easily accepted by those working in the legal domain who like to deal in incontrovertible fact and may look upon a 95 per cent confidence interval as something more appropriate to the workings of the National Lottery than due legal process.

Similarly, can chemical X actually be traced back to the factory? Just because it is in use there does not prove that it was discharged from there, a point which is likely to be strongly contested.

As cases like these develop, it becomes clear that what is being weighed is not empirical evidence but the judgements of professional experts. This tends to exasperate legal professionals who in the worst case see a carefully constructed series of arguments undermined by the apparent equivocation of their expert and at best may be left hopelessly confused by the complex issues raised in court. And the problems cannot be simply addressed by codification as per, for example, the Law Society's evolving Code of Practice for Experts.

Much could be gained from a greater understanding of the needs of the legal profession and the capabilities of expert communities. Experts must be prepared to use their expertise not only to substantiate the case but also to clarify areas of uncertainty and potential weakness. They must recognise the legal need for incontrovertible evidence and keep this need at the forefront when advising the legal profession. For its part the legal profession must realise that science is essentially the pursuit of knowledge through the construction of experimentally testable hypotheses. Therefore, for any given hypothesis, there will be divergent views, all potentially valid at the current state of knowledge.

Although an expert may be impartial, he will undoubtedly favour certain elements of hypothesis over others and such favouritism may be critical in a legal context.

Changing environmental priorities suggest that the role of the expert witness is likely to grow. It is in everyone's interest that a formula be developed to accommodate scientific uncertainties expressed in the form of potentially conflicting professional judgments.

Perhaps the answer lies in a more careful formulation of the regulatory and legislative framework so that an adequate standard of proof is more readily attainable. Whether this will happen is another issue.