I was prepared to give Stella the benefit of the doubt when she first appeared and everyone was moaning about her dodgy accent. She hasn't grown on me, though - in fact, she ruins every scene she's in for me. That accent doesn't sound any more natural to me, either.
Jessie Wallace did a great accent when she played Pat Phoenix in The Road to Coronation Street, so I know it can be done by a southerner (and an ex-Eastender to boot).