Thanks for your prompt reply Craig.

I have found an answer, but as you'll see it's now led me to ask another question below.

As it turns out there weren't any other course completion conditions set, and the course completion editor wasn't immediately useful  as I didn't know the name of the user who had completed the course.  All I knew is that reporting was showing 1 user had completed it.  Going with the date from a report ( I could see from the Report that a user had completed the course on a particular date), I did a search through the logs of all users who had accessed the course for that date, and then used the completion editor to search through these users details.

What I've found is that the user had their course completion updated manually by one of our team members (I found this in the logs for that identified user).

So, to help make things faster, Is there a way you can do a search/report that shows a breakdown of course completions so we can see which ones are manually completed, so you can identify these types of users more easily?  

Cheers,

Fiona