Don't know whereabouts in the Peak District you live, but given the fact that some garden centres will probably be getting low in stocks of some seed potatoes there is safety in numbers in the Coal Aston area (Wards, Ferndale, and New Leaf garden centres all within a couple of miles of each other., the second 2 almost next door to each other.)
Last year all were selling bagged and loose seed potatoes, and he first 2 both have cafes if you get hungry or thirsty. (Didn't need to go further than New Leaf this year, so can't give you the up to date situation on the other 2.)