Are you referring to the books, "The British Shotgun" by D. J. Baker and I.M Crudgington?

Their volumes are a must have reference for the British shotgun as they list all of the patents. I have all 3 volumes and use them extensively as a reference while reading other books about the English shotgun.
I would vote for “The British Shotgun” but all 3 volumes, because you’ll have to buy their books sooner or later so you might as well get them now. smile