England woke up on Monday to the lifting of most mandatory coronavirus restrictions.
There is no longer a legal requirement to wear face masks, while limits on social gatherings have been scrapped and work-from-home guidance has ended.
Nightclubs, theatres and restaurants can fully reopen, while pubs are no longer restricted to table service.
But there are still fears that the government is coming out of the lockdown too soon, with UK case numbers currently at 50,000 per day and predicted to rise as high as 200,000 later this summer.
Boris Johnson has urged the country to proceed “cautiously”.
In a video posted on Twitter, the prime minister said: "If we don't do it now we've got to ask ourselves, when will we ever do it?
"But we've got to do it cautiously. We've got to remember that this virus is sadly still out there. Cases are rising, we can see the extreme contagiousness of the Delta variant."
On Monday, vaccines minister Nadhim Zahawi insisted the government was "doing the right thing" despite the current case numbers.
He told Sky News on Monday: “It is a step forward, an important step forward – there is no perfect time to take this step, this is as good a time as any as (Professor) Chris Whitty has said, with the summer holidays and schools being out, which will hopefully bear down on the R number, the transition rate.”
He added: “So, I’m confident that we are doing the right thing.
“I think the vaccination programme has allowed us to take this step, to take it cautiously with this wall of protection among adults in the United Kingdom."
Professor Neil Ferguson – whose modelling led to the first lockdown in March 2020 – said daily cases could reach 200,000 before the current wave of the pandemic finally peaks.
He said that could result in 2,000 hospital admissions a day, leading to “major disruption” and further backlogs in NHS services.
A number of nightclubs reopened at midnight at Monday for the first time since the pandemic began.
In Leeds, people queued before entering Bar Fibre nightclub just after midnight.
“It feels so special,” said bar owner Terry George. “People are treating it like a very special occasion, like a New Year’s Eve type affair. Freedom Eve is what we’re calling it.
“Finally, we’re going to be able to dance. That’s the biggest thing, which is kind of a little bit sad really, because we’re given back something that’s our given right, to be able to dance in a bar, in a club.
“It should’ve been something that was there much earlier than this.”
Johnson is spending today self-isolating at his official country residence at Chequers after being “pinged” by NHS Test and Trace following a contact with health secretary Sajid Javid, who has tested positive for coronavirus.
Johnson and chancellor Rishi Sunak, who also met Javid on Friday, initially tried to get round the requirement to quarantine by saying they would join a daily workplace testing programme being trialled by the Cabinet Office.
However, they were forced into a hasty U-turn amid widespread public anger at their “special treatment” while tens of thousands of people were being forced to miss work or school and stay home.
Watch: Clubbers return to the dance floor in England