Answered my own question, posting here in case it helps others. It seems this switch is a common part also used in Peugeot/Rover etc so a quick trip to my local breakers and a Peugeot 205 gave up part of it's loom for a couple of quid. They even threw in the switch :)

Good morning friendly Landy owners. I want to add the fuel cut off inertia switch to my 1968 fuel injected TR5 (don't laugh) and bought a switch off Ebay as it looked perfect for the job. My mistake was assuming it would have lucar connectors but alas, it needs the plug for me to hook it up that...