Create a large cube, put the camera inside it, and you get a blue glow (and it aint Cherenkov radiation!) Using Standard, Volumetric and Environment mapping, turning fog and haze to zero, making the light colour black, ambient black, overall skylight colour black, bias black, sky colour map black, haze colour black, fog colour black - nothing seems to remove or affect this blue glowing. I want a totally black chamber into which I can introduce my own lights, and this blue glow destroys the illusion completely. I should also mention that the cube material is the flattest, stealthiest, least shiniest material, matt black you can possibly create. What did I miss ?

This has something to do with the normals of the cube.  The normals are facing outward. The best work-around is to create a hollow box with a boolean subtraction.

Perfect, that did the trick. Many thanks!!