Sigh!

Herd immunity applies to the fact that a certain percentage (usually > 90%) is vaccinated against a specific virus.

You can't herd immunize a population by letting them get sick. What the Brits are attempting, in my opinion, is sheer madness and totally irresponsible. Even when they try to backtrack from the term "herd immunity" now.

Or, how do you think herd immunity ever worked on smallpox, or polio?

Hint: It started to work, when people got vaccinated against smallpox and polio. Before that they got sick in a very misearble way and died. It's not that they ever developed "herd immunity" on a natural way.

I also think that your suggestion to just bunker away old people in your original comment is outright offensive.