If the closest at that point was Reddish South, then I think we need to be within 50 miles (but only just) of exactly one of Sheffield or Crewe, since nothing else is far south enough.
That eliminates almost all of Greater Manchester, I think. The remaining possibilities look to be West of the WCML but south of Preston (and presumably north of ~Wigan), or else somewhere on an arc of approximately Burnley-Skipton-York-Brough.
I am sure I will be corrected if I've got any of that wrong. I've been wondering if the 'lying by omission' thing could alternatively mean that Northern don't run many trains here, but it's a really vague clue so I'm fumbling here.