I hope there is no discrepancy between the size of the root partition and the filesystem on it.
I have found the problem. ( I hope I will check out fdisk -l tomorrow. going to bed now ).
I unmounted all of the /media and /mnt partitions and found a duplicate folder called /media/etc with 20+ gigs of data in it ( using filelight ) from a while ago. Deleted all of it and got my space back.
Now i am happy

I had the same problem a few years ago i.e hard drive full, now I wonder if it has happened before.
Oh well all is good now.
Thanks for all of your help
Dave