Well the MRI scan is done and I now know why my knee has been bothering me. NB the pain predates any running activity.
The meniscus is damaged but not enough to be operated on. Strangely when I run it doesn't hurt and since I started in September my knee has felt better. It hurts most after long periods of inactivity ie car journeys, sitting at a desk. Weighing up the pros and cons I feel that running has brought me so much benefit (sleep, general happiness, self confidence ...) that I can stand a small amount of pain.
Any thoughts ? Is anyone else running with this sort of problem ? BTW I am 49 and have reached the end of Week 7.