It seems that one does have to set up an account to get the free download--just letting folks know. I presume that's why it added it to my "basket" (that would be the "cart" in US parlance) but then there was no button to go to the basket. Because I had not logged in.
Interesting to see that Matthew Waterhouse wrote the script. I remember him from Dr Who as Adric in the late 70s and early 80s. I know he's acted a lot in Big Finish productions.
cheers, H.