Hi Seachnasaigh. Thanks, yes I have tried that already. It was set to "Quality", so I changed  it to "none".

I've also tried disabling the displacement option and also the back facing polygons checkboxes in render settings.

I think I've tried everything listed here... apart from correctly adding an AO node.

But, if it isn't the AO, I'll no doubt just have overlooked something silly ;-)