BINGO! Thanks to the very knowledgeable owners of Ace Brooklands, my ABS is now fully functional! The ABS ECU and associated diagnostic bits are indeed behind the heater box, beautifully hidden away just to make the job that little bit more interesting! Everything checked out part from a broken wire which was the root cause of the problem. Thank you everyone, especially Paho! I might even treat myself to a celebratory beer or three this evening!
Next task, get the hood electrics operational once more!