I went and saw the physio and he reckons there's no bio-mechanical problem. It looks like the nerve is pretty enflamed and that it's a case of IT Band insertion. He acupunctured my IT bands (feels a bit like a big static shock and is nothing at all like I imagined) and said it'd feel like I've been bruised for the rest of the day, but to be honest I felt fine. My IT band on the left leg was so tight that he said "it's supposed to be like a trampoline but I wouldn't want to get on that trampoline 'cause I'd end up on the moon", then proceeded to have his needle bent by my IT band 'cause it's that blimmin' tight. He also gave me some exercises to do 3 times a day (to strengthen my VMO - yes, I was totally right to try doing that, but I'm a "global mobiliser" so they don't engage that easily 'cause the other muscles just take over where at all possible - and glutes) and to try a test run at the weekend.
Parkrun tomorrow morning it is then and I'm to text him with feedback on it. If my knee goes *poof* I'll need to go back in ASAP for more acupuncture.