Thanks for the advice.

I've got an appointment to see my Doctor next week (had to wait a week for the appoinment!). I'll try and get it sorted by my company medical insurance ( a lot lot faster than the NHS).

I took Ibuprofen tablets when it really flared up. I can't keep taking them as I've had a stomach ulcer in the past and been recommended not to take Ibuprofen. I'll try some gel instead.

My wife suspects a muscle imbalance which is causing the kneecap to not move properly and cause irritation. I also badly overpronate on that leg.