Elisabeth Longford refers to the circular in "Welliington : 'The Years of the Sword'
https://archive.org/details/wellingtonyearso00long/page/368

And Rory Muir discusses the circular and responses to it in 'Wellington: The Path to Victory' and in his online Commentaries:
http://www.lifeofwellington.co.uk/commentary/chapter-29-madrid-and-burgos-july-november-1812/