@peterw , I get driven to distraction by some of these medical people!!!!!
MS is causing your balance/gait problems. Our brains are very good at automatically compensating for any related weaknesses. However, this auto-compensation can introduce very bad practice, which can put unnatural pressure on joints and muscles. This leads to pain!
So, MS is probably the culprit, but indirectly.
Ask your MS Nurse to refer you to Neuro-physio for an assessment. They will check your posture/gait and prescribe simple exercises to correct any problems.