This idea of an early lockdown that suppressed the virus is from the realm of the fantastical, not least because SAGE were not especially keen at any point. Lockdown-fans should note that it was the government who sent us into lockdown, not the science; basically you owe Boris a big one.
Even if the lockdown had been more rigorous for the general public, most of the transmission was in the already-locked-down environments of hospitals and care homes - there's no way their structure could have been changed in time. Oxford suggest reinstating the 'fever hospitals' of yore, which is a good idea for the future.