The National Monuments Record’s archives catalogues, with some images, describing over a million photographs and other archives, are now online at http://www.englishheritagearchives.org.uk.
This is a useful step forward and they say “We’d welcome feedback, so please use (and encourage your searchers to use) the site feedback link to let us know how we can improve it!”
Entering “windmill” as a search term and only looking for records with an image attached, produced 199 hits mainly from the second half of the 20th century (including some for Windmill Street in Manchester). Mill enthusiasts are likely to be disappointed; although there are a small number of interesting images, most are of other topics (eg horses or cattle) with a small image in the background.
The advanced, more specific, searching could be very interesting, but requires a little patience as 1 million records are searched. The enlarged images are only 450 pixels wide, ie just over half the picture size provided on the Mills Archive site.