Derbyshire is where using counties to build regions falls down. North Derbyshire is definitely in The North, south Derbyshire is defintiely in The Midlands. The border seems to be somewhere around the Chesterfield-Buxton line.
The same could be said of Staffordshire - I have always held that there is a line somewhere just north of Uttoxeter between north & south. Leek feels very northern to me where as Lichfield certainly does not.