Questions worth 6-8 marks are going to be on topics that you can write a lot about...and the answers should be pretty detailed. You shouldn't worry about not having enough to write about. You should be thinking about how you're going to structure your answer...
I suggest that you write in paragraphs. For some reason a lot of people I know do not write paragraphs. It makes me go...WTH?!
Writing one main idea for each paragraph is going to make it easier for the examiner to mark your answer. You might even find it useful to make a quick plan next to the question. Spending 1-2 minutes on a plan is much better than spending 5 minutes thinking about what to write next.
Legal Studies is a beautiful subject. Examiners will look for places to give you marks. But you have to make their job easier! For questions worth 6-8 marks...it's virtually impossible to make 6-8 main points in 12-16 minutes. What you need to do is enhance the calibre of your discussion. Make your answers richer by adding examples (but don't spend too much time on this!) and legal terms.
Do not leave empty lines in your answer. What I mean is that you shouldn't finish a line, then skip the next, and then keep writing. This won't make your answer seem longer...it only distracts the marker!
Hope this helps