I removed the door skin the other week and sorted out the door handle.
I think the previous owner had managed to lock their keys in the car and the AA had broken into it. There was a bill of £600+ in the service history to replace the door mechanism and the handle on that side and I can only assume it hadn't been put back together properly.
There's a circular cage that when screwed in, revolves round to keep the barrel in place tightly. It took a bit of time to understand how it should work (and a trip to the local dealership who didn't have a clue), but then it all came together.
The car is going in for an A/C service and I'll do the cam follower in the next month. I'm also going to get a DA polisher to sort out the paint work. I've already clayed, polished and sealed it, but I'm a bit of a perfectionist with paintwork so the DA should take care of that.
Thanks for everyone's input.