Exactly four years ago today, Boris Johnson announced the UK's first COVID lockdown, ordering people to "stay at home".
Working from home became our reality and people were separated from their loved ones, while frontline workers tackled a new and unknown virus.
With a public inquiry under way into how the UK approached COVID-19, many have criticised when and how we went in and out of lockdowns.
So if another pandemic struck, would we have to lock down again - and how would it be different?
Sky News asks scientists and disaster experts whether we would ever be told to stay at home again, what lockdown measures would involve - and whether the public would comply.
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When could a pandemic happen again?
COVID has often been referred to as a "once in a lifetime" event. But with more than six million estimated COVID deaths globally, the last comparable pandemic only emerged four decades ago.
HIV/AIDs was first identified in 1981 and has killed 36 million people worldwide. Prior to that, the Hong Kong flu pandemic in 1968 caused about a million deaths, and the Spanish flu of 1918 50 million.
Scientists warn global warming and deforestation are also making it increasingly likely that a viral or bacterial agent will "jump" from animals to humans and cause another pandemic.
"We're creating a situation that is rife for outbreaks," says Dr Nathalie MacDermott, clinical lecturer in infectious diseases at King's College London.
"I know that COVID was very hard for people and we want to believe we can just go back to normal and I understand that entirely.
"But the next pandemic is around the corner - it might be two years, it could be 20 years, it could be longer - but we can't afford to let our guards down. We need to stay vigilant, prepared and ready to make sacrifices again."
Dr MacDermott explains that by cutting down trees in the Amazon and parts of Africa, animals and insects are moving closer to people's homes.
And with rising temperatures, outbreaks of mosquito and tick-borne viruses such as dengue, chikungunya, and Crimean Congo haemorrhagic fever (CCHF) are happening in parts of Europe rarely seen before.
"As temperatures increase around the world, even the UK will become an area where it's possible for those types of mosquitoes to live," she says.
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How long would lockdowns last?
While there were three lockdowns in England, each several months long, Professor Stephen Griffin, virologist at the University of Leeds, argues there should have "only ever been one".
"Lockdown was an extreme reaction to a situation that had already got out of control," he says.
But if there was investment in mitigations like air ventilation in public buildings and generic vaccines and antiviral drugs that could be adapted at speed, he argues, lockdowns would be shorter and less severe.
Dr MacDermott says that until the government, scientists and healthcare workers know more about an emerging virus and how it spreads, "a lockdown would be inevitable to some degree".
Professor Adam Kucharski, co-director of the Centre for Epidemic Preparedness and Response at the London School of Hygiene and Tropical Medicine, says that if you can't contain severe infections and eliminate them completely - like Ebola in Africa and SARS-1 in East Asia - the only way to prevent a large disease epidemic is by heavily reducing transmission until a vaccine or treatment make the population less susceptible.
In the UK, it was eight months before the first COVID vaccine was administered and more than a year before it was rolled out more widely.
