Thanks everyone, great info. If I'm understanding this correctly, the "English Made" mark likely puts this after 1930 and before 1950 if that's when production ceased.

Does the mark mean it was intended for export? It's fair to assume it stayed in England if it was reproofed there in 1988. I haven't seen that mark on other Fredk Williams guns (though I haven't seen many).

A mfg date in the 1930s makes sense, it appears to be very similar to this model 860 in the 1937 catalog.

[Linked Image from i.ibb.co]
[Linked Image from i.ibb.co]