iPlayer

We have two iPads, one elderly and one fairly new, and two iPhones. Can someone please explain to me why, when I open the iplayer site on the newer of the two iPads, I have to log in with a password and username, but on the older one, and both our iPhones, I am not asked to log in and can access all the iplayer facilities. Not only that, but having put in my password and username, I then get a photo of Graham Norton with the message "we have updated our site so we just need a few more details. It will only take a minute." And if I choose not to give Graham Norton any more details? It logs me out!! So I open iPlayer on the old, slow, iPad, and Bingo! No problemo! Same with my phone. Anyone else have this?