Through experimentation, I've discovered some ways to reduce (though not completely remove yet) the ambient occlusion blotches

1. Reduce overall light level
2. Darken textures a little, and undersaturate colours a little
3. Bang all settings as high as your patience and CPU will allow!
4. No Interpolation, Full Raytracing

(Am not sure which of these changes has the most effect though)

Overall render will come out darker than desired, ubt this can be reversed by loading into Photoshop (or equivalent), duplicating the image onto a second layer which is given a "Screen" blend mode, and this restores the lightness, but a little detail might be lost.