It is better defined as people living within 30 miles of Charing Cross I think. See comment above. I'm not sure about the 20m figure as I can't find the stats j

It is better defined as people living within 30 miles of Charing Cross I think. See comment above. I'm not sure about the 20m figure as I can't find the stats just now. But it's definitely greater than 15m so the basic argument probably still holds.