I wonder if the Bridgnorth "Hartley" was in any way related to the similarly-named electronics operation based nearby in Shrewsbury:
http://www.madeinshrewsbury.co.uk/companies/hartleys
They were in the 1950s also "Hartley Baird" and around the same time also had a tie-in with the "Ambassador" and "Radio Rentals" marques.
http://www.gracesguide.co.uk/Hartley_Electromotives
Must admit, I find this sort of company-history absolutely fascinating.
--G6Tanuki.
"However hard a Badger may try, it can only ever dream of becoming a Fox".