"I am sure I have heard MacColl singing in an Irish accent"
He did - sixty-odd years ago he recorded Rocky Road to Dublin
Hope nobody ever remembers what I was doing that far back

I found Ewan's BBC voice on The Song Carriers a little excruciating at times - he was previously an actor and found it necessary to be adept in many accents - Theatre Workshop provided training for that sort of thing
Harry H Corbett (Steptoe) could speak with a plum in his mouth with the best of them, as could the landlady of The Vic, Barbara Windsor, when she put her mind to it
Jim