punkfolkrocker:
In a previous post, I mentioned leading sociolinguits Peter Trudgill , and - in the late 70s? - he devoted a chapter in one of his books to the subject of Brits singing pop/rock in an American accent.
Interestingly, and maybe not surprisingly, he discovered that the American accent influence on The Beatles weakened as the years moved on.
One thing he did draw attention to is the fact that sometimes The Beatles pronounced words in the way that they probably thought was American ( I don't think any of this was done consciously, btw ) but what came out was neither American nor Liverpudlian.
It has been said that people often adopt ( unconsciously) an accent that suits the material.
    For example, if somebody were to sing the old song "Any Old Iron", they might slip into a sort of Cockney accent because that is how they have heard the song performed.