As it happens I was looking at the blog post just the other day, feeling just ever-so-slightly sorry for myself that no-one had answered it. Well today I got an answer from an anonymous commenter. This is what they said:
"I came across this plant in France as well and was just as curious. After a bit of search I found what it was, this is an LATHREA CLANDESTINA, a really interesting plant. There is a nice article about it here:
So there you go. And thanks to my anonymous commenter. Here's a free pic that has nothing to do with anything.