Just spotted this online journal which looks like quite a good version of the Appalachian Trail experience:
http://www.skwc.com/exile/Hail-nf.html

As the Twitter updates note, Lisa and I went out for what was intended to be a 7 mile canalside walk in Brum from Spaghetti Junction to Bourneville on Saturday. However, when we reached the city centre (after about 4 miles), my knee began to ache, so I thought I was better that we called it a day there.

I saw the physio this morning and she said that I am likely to feel more pain when my leg muscles are tired (which makes sense as the day before the canal walk, Lisa and I had been to the gym). She has given me lots of exercises designed to strengthen my leg muscles and stop some troublesome movements that (when repeated ad infinitum on a hike) are causing my knee pain. Going back in two weeks, but in the meantime, it's lots of stretches, strength exercises and visits to the gym.

Fingers crossed...