It also feels much more natural to say England instead of UK or Great Britain. It sounds natural to say "Hey Igirisu!" in Japanese, but in English "Hey UK!" just sounds awkward XD So since he obviously speaks English, he would call himself/want to be called England.

Yeah, a lot of people seem to miss this :/ As he lived and the UK was formed etc I think that he would always be called England, but then allow himself to represent/be called the UK as well.

Haha, yeah totally XD Somehow I don't think he would willing want to be associated with that lot :')