...I want to point out that unless by "North England" you mean "some teeny tiny little island miles off the coast of northern England", then you can indeed buy unpasteurised raw sauerkraut online to be delivered "up north". Hit Google, search for "unpasteurised raw sauerkraut" and you get several dealers, including Amazon.....
It's much better to make it yourself.
.... But IIRC Gramma used to keep a couple of old crocks loaded with kraut, pickles, etc. It was very common to see grey and or green molds. She would just rinse everything off before it went on the stove.We all grew up healthy.
I haven't a clue what the difference is with 'raw' or um-pastuerized kraut.