Does anyone have a link to an actual policy document explicitly stating the UK's herd immunity policy? The link is a tweet from a random guy. Herd immunity is

Does anyone have a link to an actual policy document explicitly stating the UK's herd immunity policy? The link is a tweet from a random guy. Herd immunity is the default, and it's also being pursued by the US, despite statements to the contrary. So I'm not sure there would actually be a document, but maybe it does exist.