I have struggled with this for years and find the topic depressing. I have been to a lot of singing classes in the folk area and have always had the folk police tell me I should sing in my own accent [Durham/Newcastle]. In fact about 10 years ago a couple of prominent musicians [one from the 50/60's generation and one more recent] insisted that I should not sing a song outside my own accent so I should not be singing some of the songs I do. However, I am an amateur who sings songs I like because I like them in the accents I first heard them in and I do not just do traditional English/Scots/Irish folk songs [and most country or americana songs sound daft in a North east accent]. I do not mimic them exactly but I have a reasonable facility with accents and can do an interpretation which the people who listen to me seem to like. So do I just give up because I can't meet the expectations of some of Ewan McColl's disciples? Luckily most of the people I sing with and to are also amateurs who just like the music.
Sorry if that sounds like a rant - good luck to anyone who wants to sing out.