I added the .htaccess file in the WP admin folder as instructed.
It successfully created a second login to get to the WP CMS Admin page.
However, I worryingly just found from a customer that they were locked out of two of my public pages.
I hadn't noticed as I'm usually logged in. But I tested it and she was correct.
For two pages you were required to submit the htaccess credentials to view the pages.
Both of these accessed content from outside of the wordpress install. One from an external mysql server via Xdata plugin, and the other from a folder in my domain, outside the WP install via an iFrame.