I'm miffed birkmyre - just went to try out my new bike. Got it downstairs (live in a flat where the bike is in Manchester), cycled round to my car to get helmet (which is in a secure parking area) and fell off. Have no idea how either, but think that the handlebars weren't secured enough (bike is a fold up hybrid). So I wheel bike rest of way to car. Get helmet out, then have to lock bike up to go back to get allen key thingy to secure the handlebars. Lock bike (to save carrying back up to flat and then back down again), walk back to flat, get thingy, walk back to bike, secure handlebars, then go to ride it.
It is at this point I notice that the chain has come off and I don't know how to put it back on 
Hope your day is better than mine!