Hello John
I have followed your link on how to create a screen shot - a first for me - so thank you for that! I think I am starting to see where I may be going wrong, or at least I hope I can see! My video was shot using my Canon HV30 - 1080i - 25fps - Pal. Clearly - I am neglecting to input the correct settings at the outset, so would that be the capture settings?
During the time spent "fumbling around" for an answer I selected a clip in the timeline > right click > field options > processing options. "none" was selected. Once I changed this to "always deinterlace" the problem seemed to disappear. I'm sure to everyone else it is obvious but I know I have missed something pretty big!
Thanks again