Shoppers have queued to get back into stores and drinkers enjoyed early morning pints as lockdown rules were eased in England.
Midnight haircuts also took place as some consumers wasted no time in taking advantage of the latest relaxation of COVID-19 restrictions.
Wintry weather in some places failed to deter the hardiest as they flocked to high streets, salons, gyms and beer gardens – some clad in thermal underwear to withstand the cold.
Figures from data company Springboard showed that, by midday, footfall at UK retail destinations had doubled compared to the same period last week – and was more than four times higher than a year ago, when the first lockdown was in force.
However, the measure of shopping visits was still 36% lower than the corresponding period in 2019, indicating that beleaguered high streets were still far less busy than before the pandemic struck.
Prime Minister Boris Johnson urged the nation to "behave responsibly" as non-essential shops, hairdressers, salons, outdoor attractions and gyms, as well as outdoor areas of pubs and restaurants, reopened.
Elsewhere, in Wales, people can also visit non-essential shops and travel across the border to other areas of the UK from today. In Scotland, non-essential stores will open on 26 April.
Meanwhile, people in Northern Ireland are now allowed to meet 10 others outside as the "stay at home" order has been scrapped.
As rules were eased in England on Monday, some pubs and hairdressers opened at midnight, while shoppers were queuing outside stores early this morning as high street retail opened up.
Shops are allowed to open from 7am-10pm to help prevent overcrowding.
At department store chain John Lewis, glassware and gift items were among the most sought-after products as consumers returned to the aisles.
Helen Dickinson, chief executive of the British Retail Consortium, said it was a "big day" for non-essential stores.
She told Sky News that around £30bn of in-store sales have been lost during the COVID pandemic so far and shops are now "desperate to welcome their customers back".
Ms Dickinson said shops would have been focusing on the safety of their customers in preparations, but the public also has a "part to play" in following the guidance.
The retail sector was one of the worst hit parts of the economy as the UK experienced its biggest slump for three centuries last year, shrinking by nearly 10%.
Now, businesses hope that record levels of savings stashed away during lockdowns will help fuel a bounce-back.
Some people welcomed today’s relaxing of the restrictions by visiting pubs and salons at midnight.
Emma McClarkin, chief executive of the British Beer and Pub Association told Sky News the day was a "first small step in a very long journey to recovery" for the sector.
She added: "The pandemic has been a really devastating time for all those in the beer and the pubs sector [and] … we won’t be able to enter any sort of profit until all restrictions are lifted."
Meanwhile, a pub is Coventry is under investigation by the local council after a large crowd lined up outside for the midnight opening.
Videos posted on social media also showed more than 100 people in thick coats queuing outside the The Oak Inn this morning.
A Coventry City Council spokeswoman said: "We will be investigating any venue reported to not be following [the] rules or having difficulties with large queues or unmanageable amounts of visitors."
Elsewhere, London-based at-home beauty salon Secret Spa started doing appointments at midnight.
Co-owner Emily Ewart-Perks said the demand is so high, today’s bookings are set to double the company’s best-ever takings to date.
"We realised we had quite a few regular clients who we weren’t able to book in on the first day back, so we thought ‘why don’t we open the first moment we can?’" she said.
"It’s so amazing. It’s just been such a long time coming."
Boris Johnson has his haircut on Monday morning, his spokesman said.
Other businesses are also expecting a welcome boost following months of closures.
Marika Smith, general manager of Hough End Leisure Centre in Withington, Manchester – one of the thousands of indoor exercise spaces reopening – said they have seen a "big uptake" in new people booking to visit the centre.
Ms Smith said: "All of the swimming is fully booked, you can’t get on any, and the same for the busy parts of this evening, 6-7 o’clock, is fully booked.
"We have had quite a big uptake of new people coming to the centre, which I think could be down to people realising that they have spent a lot of time at home and just wanting to get out and about and doing something."
And the boss of Chester Zoo, Jamie Christon, told Sky News the park has sold out of tickets today and is largely booked up for the rest of the week. It follows a loss of £11.5m during the pandemic.
Despite the relaxation in lockdown rules, social mixing indoors will remain heavily restricted, with around two in five adults yet to receive their first dose of a COVID-19 vaccine and the vast majority yet to get both.
"I’m sure it will be a huge relief for those business owners who have been closed for so long, and for everyone else it’s a chance to get back to doing some of the things we love and have missed," Mr Johnson said.
"I urge everyone to continue to behave responsibly and remember ‘hands, face, space and fresh air’ to suppress COVID as we push on with our vaccination programme."
The need for continued vigilance was underlined by former government chief scientific adviser Sir David King, who highlighted a surge in cases in Chile despite a successful vaccination campaign.
He told Sky News: "From the point of view of the population itself, we’re all dying to get out of lockdown.
"From the point of view of the epidemic, I think it’s all a little bit more worrying."
He added: "Chile is a country where the rate of vaccination amongst the population was third highest in the world – they were ahead of us in terms of the number of people who have had the vaccine – and they’re suddenly now into a third wave."
Modelling by government advisers in the UK has suggested that Monday’s relaxation will not result in a surge of cases that would put pressure on the NHS, but it is "highly likely" that there will be a further resurgence in hospital admissions and deaths after subsequent steps along the roadmap out of lockdown.
In response to the easing of restriction, the Metropolitan Police said it will be "stepping up" patrols in high footfall areas from Monday.
Jane Connors, the Met’s Deputy Assistant Commissioner, said: "The Met is ready to welcome back people to the streets of London. We will be stepping up our patrols to busy high footfall areas, to look out for everyone’s safety and to disrupt any criminal activity.
"Of course, where we need to take action against those who dangerously flout the rules we will do. While the case rate has declined in London, we have seen the concerning position in northern Europe. It is important that we all stick to the rules so further lockdowns, or restrictions, are avoided."
The next step in easing lockdown in England, as per the prime minister’s plans, is the 17 May, when socialising indoors will be permitted under the "rule of six".
All restrictions are due to be lifted by 21 June.
However, this will only happen if experts advising the government judge that the vaccination programme is safely breaking the link between infections and deaths.
After three months of full national lockdown, the government said on Sunday that a further seven people had died in the UK within 28 days of a positive COVID-19 test. Another 1,730 lab-confirmed cases were also announced.
Around 61% of adults have received at least one dose of the vaccine, according to official figures suggesting that more than 32 million people have received a jab. More than 14% have had both doses.
Mr Johnson welcomed a "record-breaking day" for second doses after figures reported on Sunday stated a rise of 475,230 jabs.