I've seen stuff on this before. It is natural to sing with an American accent:
Mick Jagger, Elton John, Rod Stewart, Ed Sheeran, Phil Collins and George Michael all grew up in or near London and have very recognizably British accents. Once on stage, they sing like someone who grew up in New England rather than old
Even American singers, if they have, for instance, a strong “New Yorker” or perhaps a “Hillbilly” accent, will also tend to lose their specific accent, gravitating more towards neutral English, unless they are actively trying not to, as many Country singers might.
For the specific details, we’ll turn to linguist and author, David Crystal, from Northern Ireland. According to Crystal, a song’s melody cancels out the intonations of speech, followed by the beat of the music cancelling out the rhythm of speech. Once this takes place, singers are forced to stress syllables as they are accented in the music, which forces singers to elongate their vowels. Singers who speak with an accent, but sing it without, aren’t trying to throw their voice to be deceptive or to appeal to a different market; they are simply singing in a way that naturally comes easiest, which happens to be a more neutral way of speaking, which also just so happens to be the core of what many people consider an “American” accent.
To put it in another way, it’s the pace of the music that affects the pace of the singer’s delivery. A person’s accent is easily detectable when they are speaking at normal speed. When singing, the pace is often slower. Words are drawn out and more powerfully pronounced and the accent becomes more neutral.
Another factor is that the air pressure we use to make sounds is much greater when we sing. Those who sing have to learn to breathe correctly to sustain notes for the right amount of time, and singing requires the air passages to expand and become larger. This changes the quality of the sound. As a result, regional accents can disappear because syllables are stretched out and stresses fall differently than in normal speech. So, once again, this all adds up to singing accents becoming more neutral.
http://www.todayifoundout.com/index.php/2013/08/why-british-singers-lose-their-accent-when-singing/
They gave Kate Nash as an example of one keeping their British accent. You can hear the brit in her voice.
And the Ramones don't sound British at all. lol. wtf