What effect on the economy do you think NOT locking down would have had?
An extra 470,000 deaths in the UK which would have completely overwhelmed the NHS (and morgues). 470,000 key workers, elderly, vulnerable dying. You reckon the economy would still be functioning fine and we'd all just be carrying on, stiff upper lip, we're British?
There'd be CHAOS. Riots and looting as a result of the massive hoarding that would have been going on, mass absenteeism from work as people took their own decisions (or were off work seriously ill) - you may remember that many companies had already closed up shop, locked down, gone to remote working etc BEFORE the Government finally mandated it. No-one would be "just carrying on", there'd be no normal operations at the NHS (because they'd long since have been overwhelmed and would be taking years longer to recover beck to normal).
The idea that everything would just be fine with the UK just carrying on regardless (while virtually every other country in the world was on lockdown) is just farcical. It's not realism, it's complete utter fantasy.
We had this with the Millenium Bug computer code thing. Thanks to a LOT of very hard work behind the scenes from a lot of computer programmers, nothing happened. (well, almost nothing - in some cases the problem got kicked 50 years down the road by tweaking some 2-digit year codes). That lead to a load of conspiracy theories saying it was all overblown, all a big hoax. It wasn't at all, the preventative measures taken stopped it from being a catastrophe. Without lockdown, we'd be in a far worse place and the economy would still be wrecked for a decade.