Thanks for the ideas guys....

The neg' isn't at fault I've got an old pefect print from which I'm comparing my new rubbish ones with.

As I said there is no light pollution...... (also no fogging on the unexposed areas of the paper).

I have thoroughly cleaned the processor.

Cross curve problem? What on earth is that?!
It doesn't look as exact as "highlights green shawdows magenta or vise versa" as you say, but I can't seem to get the clean white print inbetween the green and magenta prints.