You may be called as an "eye-witness" if you personally witnessed something happen that is relevant to the case. You may be called by either side in the case, whether it is a criminal case or a civil case.
When you take the stand, a Bible will be handed to you and you will repeat the oath or affirmation that you will "tell the truth, the whole truth and nothing but the truth". You will then be asked a series of questions to allow you to describe what you witnessed.
Your evidence as an "eye-witness" will be confined to the facts, i.e. what you actually saw, rather than any inferences or assumptions you have made from what you saw. You will then be cross-examined by the other side.
You may be called as an "expert witness" by either side in a case about a matter that is outside the ordinary knowledge of the judge or jury. For example, you may be called as a handwriting expert or as a doctor to give an opinion on something that is relevant to the case.
Your opinion is accepted as evidence because you are an expert on the subject and because the court does not have the knowledge or expertise itself to form a reliable opinion on the facts.
As an expert witness, you must also take the oath or affirmation. You will then be asked to explain why you are an expert in the particular area, i.e. to outline your qualifications or work experience. You will then be asked a series of questions to allow you to give your opinion about certain facts. Finally, you will be cross-examined by the other side.
There are different situations where you may be called as a "character witness":
You will make the oath or affirmation and then you will be asked a series of questions to allow you describe what you know of the party's character. You will then be cross-examined by the other side.
For more detailed information you should seek legal advice.
If you have a question relating to this topic you can contact the Citizens Information Phone Service on 0761 07 4000 (Monday to Friday, 9am to 8pm) or you can visit your local Citizens Information Centre.