Thanks for the question, @Everanewbie.
I was meant to run an international event in March 2020. I remember spending one weekend reviewing the publicly-available evidence, in particular the experience in Italy. Remember that? Footage of hospitals overflowing with extremely sick people? We formed the view that the UK was a couple of weeks behind Italy in terms of the impact of the virus. As such, on the Monday, we cancelled. I recall this was a good week ahead of the lockdown announced by Johnson, meaning that lockdown should have started at least a week earlier, if we were able to figure out there was a problem! But the government had been briefed for months - there were meetings in January and February (which Johnson failed to attend) to discuss what was happening. So in fact lockdown - or at least some restrictions (eg, banning flights from Wuhan) - could have started well before that.
One thing I'd also encourage everyone to think about is how people die from Covid. And by this I mean the actual logistics. Because by and large, people don't stay at home and slip away in their own beds. They get taken to hospital, and once they are in hospital, if their condition deteriorates, they get escalated through a regular Covid ward (where they might receive supplemental oxygen) to the ICU. Once in the ICU, they don't stay for a couple of days (which is the average length of time in intensive care - ICUs get lots of short stays, for instance for post-surgery care) but they stay for weeks and weeks. Hence the NHS having to expand ICU services, and health care workers from all over the system being brought in to care for Covid patients.
In my view, the reason we needed lockdown is because the NHS was at risk of being totally overwhelmed, to the point where doctors would be doing emergency triage medicine in a way that the public would find totally unacceptable. This means that, due to lack of resources and staff, doctors apply some strict rules and protocols to decide who gets treated (whether that's no-one over 60 goes to intensive care, first come first served, lottery etc). If you are interested in how this can turn out, Radiolab did an amazing podcast focusing on a New Orleans hospital alleged to have practised euthanasia on some patients following Hurricane Katrina. It's very confronting.
We are now in a much better position because of the vaccines, new therapeutics and how much we've learnt about treatment. Initially, ventilators were the answer - so much so that even Dyson was going to knock up equipment. But we cannot get too complacent, as we're only a new, deadlier, variant away from being thrown back into chaos. This doesn't mean the answer should be another long, wholescale lockdown - I agree with lots of people here that lockdowns should be a response of last resort. But it means we have to have proper emergency and contingency plans. This is the responsibility of government, including through its own pandemic planning and how it funds and supports the NHS and social care. Debates about whether you and I should wear a mask to the shops are, frankly, a distraction from this far more important point!