I think this is multi layered.
What should we have done
What could we have done
What can we do now.
The major problem in all those decisions being the impact on society and the economy.
What should we have done?
Think that's easy. Locked down earlier when we knew about this new strain and could see transmission rates rising exponentially. Tier 2 London was a major mistake.
What could we have done?
They could have listened to those on the ground telling them the RL situation. They could have realised when schools in SE were seeing mass transmission in schools and wanted to remote learn that they could have had a valid point - rather than say no and go as far as legal threats.
And in light of a document printed 4 days after term ended saying under 17's are up to 7 times more likely to be index case in a household (knowing christmas would see households in closer contact) they knew there must have been truth and decided instead to ignore it.
They also had idea of new strain.
What should we do now?
Lockdown harder. All completely non essential business needs to close and furlough provided. For example - I have a sofa on order and ordered months ago. I am getting emails it's still in manufacture although shops are shut but may be small delay.
It doesn't need to be being manufactured in a busy factory. It's not essential. Shut all the coffee shops etc that entice people out into queues. Again it's nice but not essential. Stricter measures if take out shops remain open. I've been to takeout places and you wait inside and the delivery drivers all wait inside. Unnecessary. I've stopped going. Curfew. 8pm until 6am. Those working in shops etc get a special letter printed by employee that can be accessed from government website but on company paper so it's legit.
There's absolutely no underestimating the impact of all these options but I think we are at the point it's necessary. I think 4 weeks of absolute hard lockdown would make much more difference than 2-3 months of this current situation.