Here is something intresting:
http://www.andrewalston.co.uk/manual/p03.htm
I think only 1931 models still had such a big throttle lever:
http://www.andrewalston.co.uk/instruct16-20/p02.jpg
Older ones had a smaller one.
Idiotic thing: I was Gooogled directly for manual for those cars (and "Lanchester" LD10)... nothing. Googled another things about those cars, found results.