My thanks to @manton for resetting my blog that I had broken. I mean really broken.
How - because I was trying to be clever with the footer - and I clearly was not!
Now back up with the Tufte Theme - courtesy of @pimoore running as it should - and the footer kind of organised as I wanted.
Next step - now I understand the very clever nuances that Pete has included in the theme - is to reintroduce some of the emphasis I want.
I am slightly hesitant to rely to much on some of the shortcodes he has added (yet) since those short codes (I presume) will only work on this template?
More diving needed.