I dug and dug until by the off chance I remembered my last second hand bookshop purchases. Sitting amongst this lot was "Battledress: The Uniforms of the World's Great Armies - 1700 to the present."
What a little gem this book is. Apart from it now being a good read, it has solved some of my problems I had with equipment. The illustrations aren't the quality of Osprey publications, but they are good enough to help out the uninformed.