Rather than another lockdown, maybe a review of shielding criteria, with special consideration and support instituted for those who are more likely to suffer badly, or die from Covid, would be better. It wouldn’t be foolproof, and support would depend upon measures that helped maintain mental health too.
It’s very hard to retain social contact for people who are vulnerable and ensure contacts don’t transmit the virus (no tea and crumpets with certain politicians) but this is where everyone would need to be prepared to adjust their behaviour.
I think, on reflection, this is as likely as a Moonshot.