Have you ever been to Bristol? The way they pronounce "half" reminds me of American accents. Not "half" like the Queen's English, not "haff" like some places oop norff, but "haaaff" said with kind of a wide mouth. It perhaps makes sense, as Bristol was a port town that a lot of early immigrants to America started from.

That and Scottish kids. I think they watch so much YouTube these days (particularly up in the middle of nowhere) that they pick up a twang of American.