So after reading a number of threads a couple of weeks ago about this book being sold on Waterstones, I sent them an email asking about it and around a week ago I got this response.

Thank you for contacting us, and for making us aware of your concerns relating to this title. 

We receive title information for our database through an automated feed from Nielsen Book Data, the main data aggregator for the UK booktrade. Books are notified to Nielsen by publishers and distributors in the UK, including those that are self-published.

 With the size of the catalogue numbering into the millions, we go to great lengths to exclude racist and otherwise unacceptable titles. Inevitably, some escape this scrutiny and these are removed as soon as they are noticed. 

"The Transgender-Industrial Complex" will be investigated without delay and removed if found to be unacceptable

​

I have just checked and the book is already gone. There is not a single trace of the book on the Waterstones website anymore, so it does seem like they are not actually curating and approving books when they are added and they will remove books like this if necessary thankfully, although still disappointing that it slipped through.