At the risk of jumping on one of these Jetpunk hobby-horses, England isn't really a first-level subdivision of the UK as it has no political or legal existence. It's not unlike saying New England is a first-level subdivision of the USA. The most populous subdivision of the UK is probably Scotland, which would make a more interesting question.
Unfortunately if it's not Scotland then it's most probably London, which wouldn't :-S
I get what you are saying. It makes sense. I guess England isn't a true first-level sub-division in the same legal and administrative sense as the other sub-divisions on this list. However, it think most people would agree that it is one in a historical, ceremonial, and national(ist) sense--after all, England has its own distinct national identity, clearly delineated borders, its own flag, even its own football team, all separate from the other constituent countries of the UK! By contrast, New England doesn't have any of those. But you do raise a very good point. Thank you for pointing it out. I'd love to know what the official JetPunk position is on this matter.
Unfortunately if it's not Scotland then it's most probably London, which wouldn't :-S