OK, avoiding the Peaks you've got two choices:-
a) South of the Peaks by going via Preston, Wigan-ish, Stoke, Uttoxeter, Loughbrough, Melton Mowbray, Bourne, Kings Lynn.
Or a bit more Northerly going via Leek and Ashbourne but the closer to the Peaks you are the hillier.
B) North of the Peaks (sort of) by going Preston, Skipton, Ilkley, Otley, Tadcaster, and into the flatlands of Selby, Thorne, Gainsborough, Lincoln, Garwick, Fosdyke, Kings Lynn.
Can't comment on either route as I've not done them. Someone with local knowledge will be along in a minute.