Oh dear, so many of you are missing the point OR, as I have mentioned already, falling in to the " suspension of disbelief" syndrome.
If, in the UK, a fellow worker, a Brit, walked in to work one day and started taking in an American accent, and carried on forever, I'm sure you would find that, at the least, rather bizarre BUT if the majority of UK/Irish singers perform in a pseudo-American accents that doesn't raise an eyebrow. Very strange.

AND, talking about missing the point, what is Brakn getting at when he writes the following:
    "Oh dear, I feel a bit limited now! I'll have to search for songs done in an Altrincham accent"
Please explain what the above means...in the context of Brits singing the blues in a phoney American accent.