Sorry, I probably should have kept my post more concise and not started rambling about my partitions! The problem I have is that I can't mount the disk at all, SNAP says "Partition doesn't exist, cannot be mounted."
It seems like a linux problem to me rather than snap - If I do ls /dev/disk/by-id
I just get one entry for the drive, should I get part-1 part-2 etc?