From Chesterfield:

the Red Lion on Whittington Moor has Old Mill Brewery's mild always. It's my tipple of choice (a) because it's cheaper than the bitter, (b) because I strive to keep the traditional beers alive (I'm working hard on it), and (c) because when it's good it's good. BUT... it's very variable. Chesterfield is not a great mild area, and I suspect Maureen doesn't sell quite enough to keep it at its prime.

And if you're in the area, try Brampton Mild. Named after the product of a long-defunct brewery, this is a really excellent pint, but it's much stronger than you'd typically expect mild to be (ie og between 1030 and 1035). The "new" Brampton Brewery does a whole range of very good beers; Golden Bud has a very good reputation (justly so).