It's an explicit part of the UK's strategy, it's been pointed out throughout this thread.

Also, why would that be less viable than locking down all of society the way for example Italy has done?

Yeah, I know that's the UK strategy, that's why I asked if there are any examples of it being done, because it doesn't seem plausible to me. For starters if everyone is out getting infected rapidly, who will be taking care of the vulnerable people?