The logical route (M74, M6, M42, M40, though if you can take the M6 Toll after J11 on the M6, you're well advised to)) gets you round the nasty stuff more efficiently than any other and takes you close enough to nice places to detour relatively easily ("relative" being the important word here).

Don't underestimate how much travelling time is swallowed up in getting to, and having, "about an hour"'s visit in a major conurbation. EXCLUDING that time, it'll take you 8-9 hrs or maybe a bit more, including comfort stops, but no other stops, from central Glasgow to central London

En route, the major things you pass are:
- the Scottish lowlands, between Glasgow and the border.
- the English Lake District
- Liverpool (infinitely more attractive than Manchester, with more conservation grade buildings and free museums than any city in Britain except London. Especially attractive if you avoid the Beatles nonsense)
- the Ironbridge complex near Telford (access via J11 of the M6 to the M54). Where those bits of the modern era than didn't start in Liverpool started.
- the Cotswolds (depending on where the great aunt is, either get onto the M5 from the M6, then exit J6 onto the A44, and follow till you get to Oxford, or exit the M40 at J15, possibly visiting Stratford, drive to Chipping Campden, then on to Oxford)
- Oxford

You can't possibly manage more than a third of these suggestions. You can also try driving from Manchester to Bham through the Peak District.