I think I'm finally giving up, on trying to solve the squeaky left hand crank, on the commuter. Over the last couple of weeks, I've tried almost everything, but I've come to the conclusion that the crank is distorted enough (but not visibly) that it's going to creak regardless of everything I can reasonably try.
Whilst judicious use of a file on the crank tapers will probably work (inside, so not really a taper, but you know what I mean!) , I suspect it's going to be a lot faster to find the spare left hand crank, that I know that I have somewhere, rather than spend two weeks repeatedly adjusting the shape !
The noise has gone from irritating, to really really irritating, for 12 miles.
On the plus side, by pushing slightly harder on the left hand pedal, I can make a completely unignorable sound, that even the stupidest pedestrian can't fail to notice.