Case law is the law as established by the outcome of former cases.
Retrieving UK case law will involve deciphering the law citation. Law citations typically look something like this:
The capitalized letters appearing after the year will help you determine where you need to search.
In the cases above, search for just the letters in Cardiff: UKHL or EWHC QB. The Cardiff Index to Legal Abbreviations will tell you what those letters mean--in these two examples, United Kingdom House of Lords (UKHL) and England & Wales High Court Queen's Bench (EWHC QB).
Knowing this information will help you determine where to find the court's opinion.