"Folk singing aside, the majority of people who sing in England sing with a contrived American accent! "

Any contrived accent sounds just awful to me! Whatever the song and whoever the singer. But most especially when I've accidentally done it myself.

I learned one or two Irish songs off recordings by Irish singers, and it took recording myself and listening back to actually hear that I was accidentilly slipping into odd Irish accenting at moments.
And it sounded absolutely crap! Needless to say, that one has gone on my 'watch for that' list.

"Sing in your own voice", was one of the first ever pieces of advice I was given regards singing traditional songs. Friends who have heard me singing, commented that I "sound like no-one else", which is I think a good thing because it means that I've taken that bit of advice to heart and have learned to sing in the voice that is fully natural to me without picking up much noticable 'colouration' from those I'm learning songs from.

I'd encourage anyone else to take the above advice seriously too, because, it not only adds 'truth' to your song (IMO), but also compells a 'trust' in oneself that you have exactly the voice you need, to do sing this song your own way.