Its always open to interpretation. For example people will argue about the amount of time it takes from infection to hospitalisation, since that makes quite the difference as to whether changing trends in various graphs can be attributed to lockdown and other forms of social distancing. The timing stuff is further complicated by the fact that according to various mobility data the government sometimes show at the press conferences, lots of people did not wait for the government to announce a lockdown before they started changing their behaviour in dramatic ways. The lockdown started on the 24th of March but behaviour stated changing massively a week earlier than that, on the 17th, the day after Johnson advised people to avoid pubs etc (but still some days before he ordered them to shut).
Here are some hospital admission numbers for England:
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Of course it is not possible for me to absolutely prove that these number peaked on the 2nd April and then declined only because of lockdown & social distancing. But it happened within the timescales I would have expected, I am not likely to write this stuff off as a coincidence myself.
There were also signs that the authorities were deliberately increasing the bar for hospital admissions during the period of rapid increase in cases. There was a story, which I cannot find right now, about how in London they increased the score a patient needed to go into hospital, from 5 to 7, for the crucial period and then downgraded it back to 5 once the moment of maximum pressure had passed. Other aspects of the governments 'stay at home' communications also seem to have made a big difference to how many people sought treatment, so quite a lot of people ended up dying at home rather than going to hospital like they should have. And of course policy on admitting care home residents can also make a large difference to the numbers.
I'm reasonably sure that various establishment scientific and medical figures were shitting it big time between mid March and early April. They realised that their timing was a bit wrong (maybe a model got the explosive growth phase details wrong) and then had to wait several weeks to see whether things would hit the 'lockdown induced peak' before the system was overwhelmed. They just about got away with it, but thats no consolation to all those who died who would not have died if we had been 1 or 2 weeks earlier with the social distancing & lockdown measures.
Mind you, if lockdown had been done with better timing then we would have avoided the staggering number of deaths seen, and that would have given even more people reason to claim that 'see, it wasnt that bad, lockdown was an overreaction'.