.................to find out if someone is serving a prison sentence? My mate suspects that a family member has been given a prison sentence. It hardly seems appropriate to go asking his parents or family if he's inside. Thanks.
Your mate could contact the Prison Service, stating that he understands that his relative is in prison and that he'd like to contact him. (If the relative isn't in prison, HMPS would simply tell your mate that they had no trace of him).