This just isn't true. When I did a bit of research on this film it was made very clear to me that the golden rule was that the celebs are told nothing until they made the discovery on camera. Of course it's all researched behind the scenes beforehand.
Many thanks for this and your previous posting.
Sadly, it seems many people just read the title and not even the last post before presenting their subjective opinions.
"Some people" have read the entire thread, thank you

However, it has become quite clear in this thread that Ms Rantzen did already know quite a lot about her grandfather, Montague Leverson, and there was quite a lot that was only a Google away, so even if the makers do have a golden rule about telling the celebrities things in advance, they are not being totally honest about revealing the depth of information that the celebrities already knew.