So much misinformation in this thread - largely due to the lack of accurate scientific coverage in the media.
The basis for everything the UK did last Feb/March was a misguided belief that we needed to achieve a kind of "natural" herd immunity. (This is scientifically implausible incidentally - see Manaus, Brazil).
That is why you had the talk of "too early to lockdown" - the plan was to let the infections BUILD UP until it reached a level the NHS could just about cope with, and THEN try to limit it rising further. In this way, the idea was that the virus would infect all the non-vulnerable as quickly as possible so the country could then open up again. NB, they also forgot when constructing this strategy to actually arrange protection for the vulnerable.
In short, it was just about the most unscientific based approach imaginable and entirely down to Whitty and Valance disregarding ALL the scientific reports flowing out of China (the nature of the threat had been known since late January and little has changed in the subsequent 14 months), disregarding the pleas from the WHO to test, test, test, isolate the infected and track contacts, and presumably assumed that British pluck would mean that our HC system would cope better than Italy's (actually superior) one had.
Many many scientists in the field of medicine were fully aware of the problem and we all believed that SAGE would have a responsible plan. It was the end of February before it became apparent that they didn't - I remember the shock I felt, the day they announced they were suspending community testing for the virus.
So yes, most of the UK's deaths could have easily been avoided. It would have necessitated a ban on unnecessary foreign travel - tests and quarantine for anyone returning home and actually putting a Test, Track and Trace system in place months before they did like Germany did. We'd still have had virus cases, but it would have been largely limited and aside from large events being banned, the rest of life could have been largely normal with the occasional short lockdown like they have had to do in Australia.
NB, Despite detesting Boris, I don't blame him for this - we EXPECT a government to follow the advice of their scientists - they did. SAGE were the ones who screwed up big time.
The decision to ignore established UK based suppliers and opt for handouts for chums for PPE supplies. The decision to rush the first lockdown exit to deflect attention from Cummings. The decision to completely ignore SAGE last September (which led to a huge second wave) - THAT's what's on Boris's head.