If you're going there and back why not out one way and back the other? I personally think the west coast north of lancaster is just as scenic as the East coast which I find pretty dull and flat from leaving London to Newcastle, but makes up for it north of there. The bottom end of the west coast is also the oldest intercity railway in the world and was a pretty huge project for the time.

The Settle - Carlisle reccomendation is well worth a look, but i think it would be a long day to get to Glasgow and back.