It can be worth finding the relevant Acts of Parliament as these guide the tribunal in coming to a decision on your case. The UK Statute Law Database is online but as it is in the process of being updated you should check that the particular law you are researching has been updated.
You do not need to read the whole of the relevant Act. Usually just the relevant Sections will be enough. Cases are usually relatively straight forward regarding the law involved. The Acts of Parliament are also published as compendiums of statutes updated annually e.g. Blackstone's Statutes on Employment Law (Your local library might have a copy).
The case law (previous decisions of courts which are binding on cases which come afterwards)is of secondary importance to the Act. The case law is meant to 'explain' or interpret Acts of Parliament.
It might help you to have at least skimmed through the rules of procedure for the tribunal can be downloaded free using the following link: Rules of Procedure 2004 (Employment Tribunal) You might wish to first read the 'Overriding Objective' on Page 7, and then Schedule 1.