Traditionally I don't think most were - certainly they're much less hoppy than their North American equivalents. But more importantly, I think a little bit of dry-hopping would make for a very good beer, so maybe half an ounce for a week would be a good start.
I think I've seen a recipe or two that mentioned the same thing.
However, I think generally speaking, if you were to dry hop an English Pale Ale you'd change it from being a more traditional 'English' Pale Ale. It might turn the brew into more of an APA. Not that that is a bad thing. Just that I think the beer stops being an English Pale Ale when dry hopping. Basically its just a label attributed to the hops order than anything else.