"England" is not an export mark because we don't have them. It was a Country of Origin mark that was required by the US authorities.
Looking at the picture of your rifle, I see that it has been Proofed in London at some point after it left service. (This is legal a requirement for any non-governmental sale.)
I have no idea why some firearms appear to get into the US without pre-1968 GCA Country of Origin marks or 1968 GCA Import Marks.
So I guess that's a good thing that mine doesn't have an import mark? (least that I'm aware of) Mine also doesn't have "England" marked anywhere on it either (least where it's usually found.)