The UK CAA exams were exams that were under the control of the UK CAA. They were multiple choice with a pass mark of 70%, however there was negative marking. So for many people if you were unsure of an answer some people left it blank instead of risking loosing marks and guessing the wrong answer!
The JAA exams are slightly different. Individual countries are responsible for creating a question bank for a specific subject. Switzerland for example, is responsible for making up the Met paper. Each JAA country will extract questions from this question bank to make up an exam paper for each month of exams. Each JAA state has the right to include a limited number of their own questions in their papers so that they may reflect national standards or procedures. If you do the exams here in the UK then the papers are made up and marked by the CAA at Gatwick. The pass mark is 75% and there is no negative marking (hence the higher pass mark!).
The UK CAA exams still exist for those wishing to obtain a CPL for Balloons or Airships. Otherwise for any other type of exam you will sit a JAA Paper. (To the best of my knowledge!)