What better plan for vulnerable people is there than isolating them? You also seem to be under the impression that the plan is for no lockdown. The government has already said that there will be increasingly tight measures over the next few weeks.
I despise the current government, and have no idea if this plan is better than alternatives, but please if you want to criticise it, do so for what it actually is, not a straw man of your own construction.
I truly wish you good luck. Planning for the virus to expand (rapidly) through the younger less vulnerable population to protect businesses and provide herd immunity is what was described. I understand they're trying to walk that back now... good idea!
https://politicshome.com/news/uk/health-and-care/illnesstrea...
The actual plan and how to isolate the almost 20% of the population at high risk is not outlined here or anywhere I've seen. If you know (or anyone in the government knows) what it is, please provide a description or link. I've only seen hope... and undefined "measures".
I despise the current government, and have no idea if this plan is better than alternatives, but please if you want to criticise it, do so for what it actually is, not a straw man of your own construction.