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Doctors may be asked to appear in court in a professional capacity. As such they may be a:
The general rule is that witnesses give evidence about facts rather than opinions that they may have formed from facts. The reason for this is that it is the job of the Tribunal (Judge, Magistrate or jury as the case may be) to hear the evidence and make appropriate inferences.
Certain exceptions however allow an 'expert' give the court the benefit of his expertise, which may include his opinion where such matters are likely to lie outside the experience of judge or jury. It is for the judge to decide in each case;
- whether the issue is such that expert evidence would assist the court
- whether the expert has the expertise to provide that assistance.
A expert in giving evidence may support his opinion, gained in the course of his training and experience, by reference to relevant articles, letters etc whether published or not, but it must bear on the facts of the case as proved by admissible evidence. That opinion may be based on work by members of a team led by the expert witness, but disclosure will need to be given of the names of such team members.
In earlier decades in England a witness might be retained by either side - a defence expert or a prosecution or plaintiff's expert. Even then the expert had an over-riding duty to the Court rather than to the side paying him, in theory. More recently exact date needed this has been made more explicit.