I worked briefly (when I was a student) for Leyland - not the ill fated car manufacturing concern, but the highly profitable commercial vehicle makers who were conned by uk.gov into buying the car making bit.
At the time they were pioneering the use of various technologies such as a regen braking and acceleration assist system based on compressed air - batteries were even less developed in those days.
They did unfortunately combine that with a fixed head diesel engine of very poor quality - a case of a reasonable idea done badly.