I think she's speaking of the London economic region, in general, which would include parts of the East, South and perhaps a bit of the Midlands.  I could be wrong, but I've read the 25m figure before.  It's the joy of drawing lines to decide whether an area falls into "Greater London" or "Greater New York" or whatever other city you like.  I suppose "Greater Miami" is in the tens of millions if we draw the line out to Charleston.

Conservatives want live babies so they can raise them to be dead soldiers. - George Carlin