[AidanC]

Thanks everyone for all your help, especially Ron and Simon who have taught me a lot about my car's setup.

Simon: you're correct, there's continuity between the two terminals with the red wires.

Ron: the steering shroud is preventing me from taking clearer photos of the ignition switch wiring but I'm planning to replace or at least overhaul the indicator switch over the next few weeks. If you don't mind waiting, I'll take some proper pictures then.

On a side note, I noticed in my first pic that I had far too many keys on my keyring and that it was wearing the plastic top of the ignition key. I took off the unncessary ones and noticed that one of the unused keys is a Neiman - presumably the original ignition key. I've had the car for twenty years and only noticed this now..... It supports the idea that the ignition lock was aftermarket.