Never been to Scotland by road but some parts of the A15 from Peterborough up through Lincolnshire are pretty nice, although there are a few more speed cameras than there used to be.
From what I recall, there is a nice B road off the the right after Bourne that takes you up to Sleaford and from there another route to Lincoln.
The A15 goes up as far as Humberside and I'm lost from thereon.............................