Hey thank you Physiobob! Following your suggestion I looked up tib/fib joint mobilisation exercises. I found that doing them eased my knee pain considerably and it had been masking the pain coming from my hip.
I found that I have to do them fairly frequently, probably because my tight hip capsule keeps pulling the nerve out of line.
It looks like it's now a case of time and perseverance gradually stretching the hip capsule.
I'm still coming to terms with the fact that my body no longer looks after itself and I have to DO stuff to keep it working. I am having to learn about body parts I never knew existed and stretch them! I kinda resent all this.
I think many middle aged people feel the same and Physios need to understand that we struggle to accept being dragged into this new reality.