[Oscar in Bin (John)]

Graham, I have been having banding issues with my unmodified Nikon. Very bad on the night when it was Tshirts still at 3am!
I went back to some earlier light frames taken on cooler nights and stretched them very hard - sure enough found the same bands but much less noticeable. These better images were not an issue when stacked with the dark frames but the hot night images were unacceptable.
Radical fix - have ordered a CCD and will relegate the DSLR to widefield short exposure tripod images and imaging to create videos.