Job done.
Big QUESTION coming in a second.
I had to take the whole lot off and access barrel to remove bit of key, BUT when reassembly, dropped a bolt down near sterring column and FOUND what I believe is the imobilser sensor (it was just lying around).
The link for the ebay replacement shown below shows this part attached to the ignition part - IS THAT CORRECT, or is it supposed to be somewhere else (I was cold and couldn't get it to fit as shown in picture in ebay link and gave up for another day):
Landrover discovery ignition barrel and key | eBay shows the ring "FIT" printed on side
I am buying a new mechanism since I broke the steering column lock, and for now the sensor is tie-wrapped near the ignition, but where SHOULD it go?
Disco starts fine if I wave the fob around and dashboard light goes out and off I go - will do proper repair when new part arrives.