Competence of a witness
The person accused of the crime (the accused) is considered competent to testify in their own defence but cannot be forced to do so.
Sometimes two or more people can be charged with a criminal offence and they are tried at the same time. In this situation, the people being tried are called the "co-accused". One co-accused cannot be called by the prosecution to give evidence against another co-accused.
The spouse of the accused
If you are the spouse of the accused you can give evidence for either the defence or the prosecution in a case against your spouse (unless you are a co-accused). However, you may only be forced to testify for the prosecution against the accused in certain circumstances.
A former spouse is someone who has a divorce, a judicial separation or a separation agreement with the accused. If you are a former spouse you are treated as a spouse for offences committed before the legal dissolution of the marriage. However, a former spouse is treated as an ordinary witness for offences committed after the breakdown of the marriage.
If a witness is 14 years of age or older, they have to give evidence on oath or affirmation.
Children under 14 years of age do not have to swear an oath or make an affirmation before giving evidence. The court must be satisfied that the child is capable of giving an intelligible account of what they witnessed. Even though this evidence is not on oath, the child is guilty of an offence if they knowingly give evidence which is false or untrue.
If a witness is under 14 years of age the judge may ask to talk to them in private before they give evidence. This is done in order to assess the child's ability to give an intelligible account of events.
People with mental disabilities
You should get legal advice for more detailed information on this.