Re: How will they know it's a false alarm?
There are lots of estimates for the lethality of this virus for those who catch it.
I understand CDC in the US ( a fairly reputably institute) estimates it to be 0.26%. That's not an absolute limit, but their best estimate, with error bars (could be higher, could be lower).
UK government (i.e. the civil servants and scientists, not the politicians) estimate that lock-down will kill 25,000 people in the short term and 185,000 in the longer term in the UK. That is also a best estimate (could be higher, could be lower), and to emphasise - this is deaths caused by lock-down, not by COVID.
210,000 people amounts to approximately 0.31% of the UK population.
So to save 0.26% of the population, we are prepared to kill 0.31% of the population.
Yes, some that get infected don't die but do suffer severe issues thereafter. But also, whatever we do, some of those 0.26% are going to die from COVID, so we're not even saving 0.26% by killing 0.31%.
Additionally, crashing the economy also affects quality of life (not least the reduction in tax income which will reduce funding for the NHS for the next decade - that life saving drug? sorry can't afford it; that quality-of-life hip operation? Nope, reached our limit for this year).
Why is the life of someone that would die of COVID more important than the life of someone that has died of sepsis or a heart attack because they didn't seek treatment in time (due to lock-down), or will die from cancer (detected too late to be treatable, because of lock-down)?
Whatever the UK (or any other) government does, people will die of COVID, and will die of the measures that have been taken to stop COVID,