Watch: Boris Johnson reflects on regrets over coronavirus pandemic
The prime minister, holding a Downing Street press conference on Tuesday marking one year since he imposed the first national lockdown, was asked to share the one thing he wishes he had done differently at the start of the outbreak.
Johnson said the government under-estimated the potential for asymptomatic transmission of the virus.
He said: “In retrospect there are probably many things that we wish that we’d known and many things that we wish we’d done differently at the time… because we were fighting a novel disease under very different circumstances than any previous government had imagined.
“The single biggest false assumption that we made was about the potential for asymptomatic transmission and that did govern a lot of policy in the early days, or that misunderstanding about the reality of asymptomatic transmission certainly led to real problems that we then had to work very, very hard to make up ground.”
Health secretary Matt Hancock has said “roughly a third” of people who have COVID-19 do not show symptoms.
This would mean that at the start of the pandemic, thousands of infected people wouldn’t have self-isolated, as was the advice at the time for people with a fever or a new continuous cough.
The British Medical Journal has also suggested "that asymptomatic transmission may result in a substantial number of cases".
Hancock has previously referred to the government’s initial lack of knowledge about asymptomatic transmission.
Asked in July last year about the thousands of patients who were discharged from hospitals to care homes, he said: “At that point [at the start of the pandemic] it was not known about the asymptomatic transmission of this disease because no other coronavirus transmits asymptomatically, as my understanding.”
Meanwhile, chief scientific adviser Sir Patrick Vallance, speaking at the same press conference as Johnson on Tuesday, reflected on the lack of adequate testing in place at the beginning of the pandemic, saying it would have made a “big difference”.
“The one thing that I think would have been really important earlier on is to have much better data on what was happening," he said.
“And that would have required testing to be up and ready immediately and it would have required the ability to get that information into a source and to be able to see it."
Watch: How England is leaving lockdown