Greetings Brian, and welcome to Multitool.org. Your research is spot on, the kit you have was indeed produced in Japan, either in the late 1960's or early 1970's. Sometimes the kits were sold directly to consumers, in which cases the blade tangs were simply stamped JAPAN and STAINLESS STEEL (in the case of sales to the U.S., and ROSTFREI in the case of sales to Europe.)
More frequently though the kits were sold in large lots to companies which resold them under their own brand, or gave them away in various promotions. I've seen the kit pouches marked with the name of automobile dealerships, insurance companies, etc. I believe this is the situation with your kit. It would likely only have enhanced value to someone who collected other items marked with the London Harness Company logo.
Hope that helps!
Bob