Have now taken to throwing catnip on the sofa at night, which seems to have stopped them. Still have TriggerTrap which I will try overnight one night to see.
I do have a Linksys camera which unfortunately doesn't play nicely with my Mac, hence alternatives and the TriggerTrap was only £20, so thought might be fun!
Give me a few months and it'll be on the 'Bay... Along with one of the cats...