I have added a section to the A4A wiki on the History of Allotments. Apart from references to the national picture, I have included a section on local allotment histories, principally containing links to a number that I located on the Internet.
More local histories would help to give us a greater understanding of the allotment movement and its social context.
Why not consider writing a history of your site? The majority of sites usually have at least one or two individuals who are interested in history. It can make for a useful and interesting winter project when there is not much to do on the plot.