Not really a "must drive" road, but if you're in North Lincolnshire & want a traffic-free alternative to the A16, try Caistor High Street (B1225) from Horncastle to Caistor then A1084 Brigg Road to Brigg - the Cross Keys at Grasby does good food!
Another of my little Lincolnshire favourites is Bluestone Heath Road, from the A16 at South Thoresby to the A153 at Cawkwell Hill, just South of Cadwell Park.
Living on the edge of the Peak District, I'm surrounded by good driving (& even better riding!) roads.
Not in the UK, but close enough: if you ever find yourself in Ireland, the Healy Pass (R574) from near Adrigole in County Cork to near Lauragh in County Kerry is a definite must.
The plural of "anecdote" is not "data".