He can't be forced to give evidence. Even if the govt compelled him to court, and that's very unlikely they could do that, he still doesn’t have to give evidence. Are you seriously suggesting that an accused has to make a case for the prosecution because they don't have evidence to make the case themselves?
Asked if they had received an MLA (Mutual Legal Assistance) request for Prince Andrew, the Home Office would only say: “As a matter of long-standing policy and practice, we neither confirm nor deny the existence of mutual legal assistance requests.”
If an MLA request is granted, Prince Andrew could be asked to give evidence in the UK.
Usually that testimony would not be under oath.
However, if he were to refuse to co-operate, the Home Office guidance says “it may be possible to compel the individual to attend court. However, the witness can exercise the right against self-incrimination and refuse to answer any questions at court.”