It's pretty brutal, but simple, and (economically) efficient - if you are over 70 (well, they say that, but they actually mean 60 (and realistically, when the hospitals are overwhelmed, 45-50) - to be lowered as needs must) - we are done with you, we need the inheritance tax and houses (awesome bonus!), we can't afford the pension pot and all the charges on the NHS for your elderly care so please do the country a favour and, you know, drop off quietly, yes? You old people are expensive and we've long since spent the funds you put in so - yeah, bye. If Boris is left to continue on the herd immunity line, he is quite correct that, from what I have read, once someone has caught the virus, they will be immune for a while - but the UK will be a very young country.
Great in the long term - not quite so good for anyone with a memory of eugenics.
Over 70s can isolate or not - this will be coming back every year with the usual flu viruses - just that if they get it this year, they need to be aware they will not be getting any care from the NHS as the beds will be going to the young and viable. Harsh but . . . .