Basically, a top notch London retailer of Birmingham guns. They ran a very "honest" shop in that you got what you paid for and you got good service and expert advise. The name has Brand Value Level Three; the same Original Quality grade in the same Current Condition level gun will have a USA retail market price of half of a BV1 (Boss, H&H, Purdey, & Woodward) and 2/3 of a BV2 (seventeen makers/retailers). They were probably best known for their rifles and cartridges - they were very creative with dangerous game cartridges around the turn of the century.
Order a reprint of the 1904 catalogue ($13.95) from this site - you will learn a lot!!
http://cornellpubs.com/Templates/Jeffery%201904.htm