I found that my selection of the baking options was the problem.
Initially I unticked everything except "Ambient Occlusion" (following a few online videos) - this left the primary baking type to "Combined", with direct and indirect light and Ambient Occlusion ticked.
I bounced around online for a while before going in to look at the settings again - the direct/indirect light checkboxes bugged me because I was pretty sure there were no such things in my scene, (just my model) so I decided to click on 'combined' to see what other options there were - and then I found an Ambient Occlusion bake TYPE.
When I changed the baking type to "Ambient Occlusion", direct/indirect light (and the other options) disappeared - then it worked.
I'm guessing the direct/indirect light options in combined when I didn't actually have any lights in my scene were why it was baking black - I'm assuming the bake-type "Ambient Occlusion" option ignores lighting, or provides it's own generic ambient light for processing....either way, that's what worked for me...