It sounds like a criminal trial. Not all criminal trials are reported. If this one was, you need to know the name of the party involved; it will be reported as (e.g.) R v Smith (1986). You can then look it up in a law report such as the Criminal Law Review. These reports are normally kept in law libraries, either universities or law firms. If you are neither a law student nor a lawyer I am not sure how to go about it - I suggest you ask your local library. I am not sure whether it is possible to contact the Old Bailey direct - I have never tried.