I met a friend of a friend a few days ago in Leeds. He's from Zimbabwe, and came to the UK to study just before the shit hit the fan around 1999/2000. As the shit had thoroughly hit the fan, he decided to stay in the UK, and is currently seeking asylum.
I wouldn't have known he's from Zimbabwe. He has a stronger Leeds accent than I do.
How about this for a new rule for immigrants: if you've got a stronger local accent than a local, you're allowed stay.