The cable in question runs between the kitchen and living room. It's connectivity is Red-to-phase and sleeved earth-to-earth at both ends of the cable.

Everything else is T&E, including every switch on the downstairs lighting circuit. I'm sure it's not a 'bodge' - this part of the wiring it will have been untouched since the house was built, it's just something I haven't seen before (sounds like you have though! )

The only thing I can't figure out is where the neutral in the porch and living room comes from, as it sure as shit isn't coming from the kitchen. It must go back to the consumer unit somehow, but I'm not sure how

I've done the work I needed to do now, but is there any regulation that says I must remove it if any work is being carried out involving it, or can it stay put?

Cheers!

Neil.