When someone is found guilty of a crime, the person is either instantly sentenced by a judge or jury or a sentencing date is set. If you were not in court, you can still find out what a person was sentenced to after he was found guilty. This usually requires either making some phone calls or having Internet access.
When someone is sentenced, they can get one of four main types of sentence: discharge, fine, community sentence or a prison sentence. If you are a victim or witness in the case and have left the court before the trial has ended and would like to know the outcome of the case, you can contact the person who asked you to come to court. They will be able to give you the information on the sentence. Their contact details should be on any correspondence they send to you.
If you know the date and venue of the end of the trial then you may be able to find the result of it in the Weekly Law Reports (WLR) which are published and available on-line (usually updated monthly, ironically), or the English Law Reports (ER).
You could also call the Crown Prosecution Service. The prosecutor's office acted as the solicitors for the state in the individual's criminal case. Once you dial the prosecutor's office, ask to speak with the prosecutor who handled the case of the person about whom you are inquiring. This prosecutor will be able to answer your question.
You may also be interested in using resources from the British and Irish Legal Information Institute, which provide free online access to case judgments, laws and sentencing in the UK.
Check your local paper. If the crime was serious enough, your local newspaper may be covering the trial. You may be able to read about the sentencing information you are seeking.