I had another go and three cheers, it's come out OK this time. Sunk a bit in the middle (I suspect the tin was a smidgen too large) but it's a perfectly respectable cake that I can take to the meeting tomorrow without any shame! It's not out of the tin yet, but here's photographic proof! Next time (and there will be a next time) I will cover it over for the last 15 mins or so.
The badly mangled cake of yesterday will do fine for desserts, cut into single portions and frozen until needed.