That sounds nasty Richard. I had problems like that with my feet a few years ago and the only advice I would give is make sure you're right before you start running again, I came back too early and it took me ages to shift it.
Saturday went well, managed to finish in 8hrs 42mins for 36th place so very happy for my first ultra. Had a dodgy spell around 30 miles when I felt really sick but managed to run through it and felt quite good over the last nine miles (which are mostly down hill!).