Thanks for the replies chaps.
Changing the Motion Wrapper settings
# I wanted my camera to detect movement when just two frames showed a difference, so I set minimum_motion_frames to 2.
# also need to set snapshot_interval to 2 (snapshot_interval 2)
What you describe are global settings for motion right? I have 3 cameras installed under motion - one behaves, and the other 2 do not i.e. movement doesn't trigger them to record. The settings are identical for all of them as far as I can tell.
Think I am going to take another look at ZoneMinder, as I am not actually using motion in the correct way (I have animals so motion detectors are useless to me!); all I need is for them to record when motion is detected.