https://www.nature.com/articles/s41589-023-01349-8
I copied it from the Nature article, where I got to from the BBC link. The Nature page has the full text (I'm not logged in). I'm on firefox, is it your browser?
Edit: Oh, wait, I am logged in to Nature. But only on firefox. When I switch to chrome and try navigating to the Nature article by clicking the BBC link, I get a paywall. What exactly do you see on your side?
The top right of the PDF-alike has a link that says "what's this". and it sends me to https://www.springernature.com/gp/researchers/sharedit which seems like a service that allows sharing of links to fulltext. If I go to the url directly, e.g. by copy-pasting the URL or clicking on your link, then I do not get the same behavior. Hence, I deduce that it is probably some referrer magic.
When I click the same BBC link on chrome on android mobile, I don't get the redirect, so probably there is some User Agent stuff too.