APMReport Format (for an answer)

In question one, where you are often asked to write a report, how far do you have to go with the report format? For example, I always put the to, from, date and subject; then open with a brief introduction and will often put a basic conclusion at the end. But what about workings? Often you don't know how much room you will need for these (or for the written part of your answer). If you put the workings in the report, would that lose you professional marks? Do you have to do an appendix at the end, by going a few pages ahead in your answer booklet so you have enough room? It seems unnecessarily tricky to keep a neat format under timed conditions.