Choosing and instructing an expert is practically and legally complex and can be critical to a case's outcome. It is still not treated as a discrete subject in the new legal practice course, but its importance is beginning to be recognised.
Experts have an apparent dual loyalty. Their role is "to advance the case of the party calling them" and at the same time "to assist the court" (Polivitte v Commercial Union 1987). Steering a path between these potentially conflicting duties requires experts to balance their professional integrity carefully. If the expert evidence fails to advance the case, it will not be called. If it fails to assist the Court, it could be criticised for wearing "the colour of special pleading rather than an impartial report". (Whitehouse v Jordan  1 All ER 650 per Lord Denning MR), and be ignored.
The litigator must also choose an expert whose breadth and depth of knowledge is correctly pitched to the case in hand. It is an inexact science. A case could be won or lost over the malfunction of, say, a widget in a cooling system. A chief engineer who supervises the construction of such installations might lack the knowledge required about the widget in question; an unqualified engineer who has spent 20 years repairing such widgets might have that knowledge and so convince the court. Yet it is a brave solicitor who will reject the former in favour of the latter.
In each field, the general problems adopt particular characteristics. For example, when dealing with financial instruments such as derivatives, the usual guidelines are absent. The litigator lacks even an authoritative text book. Financial instruments are created with such rapidity that any textbook would be out of date before it reached print.
There is no comforting league table of relevant academic qualifications against which to assess a potential expert; most experts will be in their late 20s and lack the age, position and gravitas normally sought. Navigating such uncharted waters is a skill that requires both guidelines and training.
Trevor Asserson is a partner and head of the banking litigation team at Brecher & Co.