For whatever reason they wrongly thought we were 4 weeks behind Italy at that stage. The number of cases in the UK and the time it had been spreading was a lot higher than they thought.
To impose restrictions on the population to early would have backfired. People wouldn’t have obeyed them. Look at the calls to open everything up now because cases are falling and deaths are low and they huge numbers of people currently breaking the law. And look at the calls to open everything back up ASAP last summer. If we have tried to lockdown early and numbers had been suppressed, the lockdown would have been short lived as people would have assumed it wasn’t necessary and we would have still have had the deaths.
We are also a country very much about personal responsibility rather than state mandated rules. This was another issue in our response. Cheltenham went ahead because the government didn’t ban it, but it was the personal choice of the thousands who went to attend- it was obvious it wasn’t a good idea.
It was a combination of unknown virus + more cases than thought + trying to time the measures correctly. They were following the science... including Psychology.
The government have made A LOT of very very bad mistakes since which have caused a lot of additional deaths. But the ones I don’t blame them for are last March.