Sorry to hear about your drivetrain issues, plum. I had my own this morning, though less disastrous.
I set off into traffic after the level crossing, but got no power out. Neutral again. Even changing up didn't give me anything. I got to the other side of the road without incident, fortunately, and adjusted the cable tension which seemed 'wrong'. Riding on a bit, I realised there was a bit more to it, and discovered my wheel, which, yesterday, I had noticed seemed a bit biased to the drive side in the chainstays, was now definitely over to the other. I stopped, inverted the bike, released cable tension, applied chain tension, then tightened the nut. Yes, nut, for the non-drive side nut is made of Sturmey Archer Stilton, and won't catch.
I've got some dropout screws coming, which will help, but I need a new nut (and a spare - they never last long
).
And, no, I don't put mighty ape torque onto it. I'm a cyclist, and have the normal arm strength for that category (i.e. all but nil).