Hi Mo,I was wondering what was the cause of your feeling that Blakes Jerusalem is "pro imperialist English"?
I've not read much Blake, or analysis of his work, but it seems clear that his intention was, as Jerry noted above, a crie de coeur against the materialistic world as exemplified by the industrial revolution, and a desire to return to, or build a society based on spiritual values. Hardly a view consistent with imperialism, and as you say, if we must label songs, then socialist seems far more appropriate.
However you care to interperet it, it's a great song.
Pete M