cleats
First things first I guess. What pedals do you use? Have they got plenty of float? I used to have terrible trouble with my right knee when i was using Look Deltas but I switched to the Look Quartz ones which have tons of float and it pretty much sorted it overnight.
The other thing that’s really common is muscle imbalance in the knee, cycling favours some muscles over others. Simple stretching exercises and some basic Yoga can help there.
Not sure about NHS Physios…