OK, a followup. I was out in the shop and checked my English saw. The blade is engraved (or more likely stamped) with "Jos Haywood & Co" in an arc with "Sheffield" below it. To the left of this is "improved" and to the right is "cast steel". The saw has the old split nuts, so it's probably quite old. Disston and, IIRC, most other American manufacturers quit using split nuts about 1875. I doubt if England was too far ahead or behind.