@davidwaller - thanks for the advice, I've never even considered surgery but perhaps it is something to look into. Did someone advise you re. the Q factor and wedges adjustments? I only ask because my bike fitter suggested a narrower Q factor and raising the inner side of my foot to compensate for a slight flat-footedness.
Whatever you do, don't try more than one thing at the same time! Get some orthopaedic insoles, consult a capable expert in your area for it. Then (maybe!) adjust your position.
I would suggest caution when changing bike positions. Get a full bike fitting by the best person you can find. Hopefully someone trained in several fit systems and years of practice. Not from your average LBS employee of the month
Definitely good advice - I'm hesitant about changing anything because my current position is the result of 2 bike fits from reputable fitters. Problem is that none of the fitters or physios I've spoken too seemed very certain about how my position could be contributing to the ITB problems, or what I could do other than stretching to improve things. Maybe the position that is best for comfort and power might not be best for my knee?
I've been off the bike for 6 months now, stretching daily for the last 3 months. Tried going for a couple of quick rides last week and things are better, but not by much. Since then I've changed pedals, shoes and bought custom insoles, and after coachpotatobilly's post I'm going to go and check for any flexibility issues etc. that might be contributing.