I have a Purdey Bar-in-Wood 16b in stock with a grip safety. At rest, it bolts both trigger blades. Here is a photo of the external lever.
The gun dates from 1877 but I am unable to pinpoint any patent. However, this style of grip safety goes back at least to the muzzle loading era. Dasvid Baker in Volume One of the British Shotgun doesn't credit the grip safety to anyone but does mention is twice.