That "pushback", judging by its length, style and tone, didn't originate from the Health Ministry, but from Johnson's adviser Dominic Cummings, a major proponent of the initial "herd immunity" policy that would now be totally discredited if it didn't appear to be the last desperate hope, since the UK government has made no serious preparations for an emergence from the current lockdown and social isolation that doesn't involve mass infection, with the accompanying proportion of deaths.

It's the old dilemma between whether events as they've panned out were the result of a conspiracy or a cock-up. Quite possibly a bit of both. Here's Johnson in early February:

https://twitter.com/OliDugmore/status/1251462463134064645


It was born of the same demented delusion of Little Britain exceptionalism that fueled Brexit.

The other "once or twice in a generation opportunity" would be Brexit. That's evidently on the back burner for now.