Hi Colin
I had a very similar injury just after I did the Sheffield marathon but mine started with a very sharp pain down the side of my knee which stopped me dead in my tracks. After when I went for a run the pain use to flair up again sometimes after only a mile of running this is the ligament rubbing on the side of your knee,I went from running a marathons to power walking in the space of a week , sounds like you have the classic runners knee.I was lucky as I got free physio from work, she told me it would take 6/8 weeks to get right and to build my runs up slowly. I also hammered the movalat gel, hope this is of some use to you
Mick H