Miclev: Have you looked at the rail map at nationalrail.co.uk/tocs_maps/maps/network_ra… ?
I would head west to Glasgow and then south to Carlisle. Between Carlisle and Exeter, I would recommend spending some time in Chester, maybe take a look around Shrewsbury and/or Ludlow, and spend a day or two in Bath. In Devon and Cornwall, I would recommend visiting St. Ives and Totnes.
There are so many places to see that it's tough to just pick a few highlights.