Using the time honoured system of looking at the last thing I'd messed with I removed the drum to see if I'd done anything wrong. Nope, all was fine there so on to the cable. It didn't seem to be doing much at all so I set to to adjust it. Got a couple of turns on the adjuster nut then it came off in my hand. The threaded rod snapped clean off.
Another cable is on the way and hopefully it will be here in time to get it fitted and a retest done before the weekend. If things keep going as they are just now, I'll have to put Moss Bradford on speed dial.
Not wanting to end on a non positive note, I fitted the passenger seat before closing the garage door.