Thank you for this. This explains the sticky menu issue and it should be fine for me to use.
I have added the css as described but it appears to have made things a bit worse. The whole site now appears wider than the window so to see it you need to horizontal scroll. Please see the new screen shot (screen5.jpg) in the dropbox folder. I have uploaded all the orginal files to my server now too (http://www.jcottrell.co.uk/enigmatic/index.html).
Thank you for your help with this. Hopefully we can get there soon. If it is easier to deal with via email please let me know?