aow, minkin and mungus, thanks for your interest and support.
I actually picked this idea up from reading around the subject of knee injuries on the web (and believe me as this injury has been hanging around for six months or more - I've read a lot). I have the idea because the source of the pain actually seems to be under the knee and in the upper portion of the leg - the sufferer I read about had the most pain when descending stairs (me) or when bending the leg under load (me also) - in addition, the symptoms seems more familiar than those for any of the other common leg complaints.
Mungus - the joint doesn't actually feel significantly looser than the other side - however one of the causes of this problem is impact from, for example, running down hills, unfortunately unavoidable where I live!
Sports injury clinic next Thursday will hopefully put me on the right track - although going by my historical experience it'll be "rest if for a couple a weeks and take two aspirin"