Dear Flopsy,
Had a couple of further thoughts today:
First, have a look at the LDWA
http://www.ldwa.org.uk/index.php
They do social walks and challenge events over various distances. They are cheap, friendly, and there's food and drink. You don't have to join. There would be scope for starting off gently and building up gradually. The challenge events attract runners who use them as useful training runs, so you may well see people you know. I'm thinking walk steadily and not too far, walk further, then switch to running. There's loads of events and you could easily plan a gradual programme over several months.
Second, my wife was chatting to a lady runner today who is post op, several years ago. We don't have her details, but I possibly know someone who does.
I'll try and see if she's interested in contacting you on the PM side of the house.