For the first time in months, pub gardens, shops and hairdressers are reopening in England, as rules are also eased in the rest of the UK.
Some pubs and salons opened at midnight, with one landlord saying there was a "sense of celebration", and shoppers queued outside Primark stores.
Prime Minister Boris Johnson has urged everyone to "behave responsibly".
Northern Ireland's "stay-at-home" order is ending and some rules are also being relaxed in Scotland and Wales.
The PM had planned to have a celebratory pint to mark the measures easing, but that has been postponed following the death of the Duke of Edinburgh on Friday.
Snow showers and chilly temperatures in parts of southern England appeared to do little to dampen enthusiasm for outdoor pints or early-morning queuing for shops and salons
Nicholas Hair, landlord and owner of the Kentish Belle pub in Bexleyheath, south-east London, said there was a "sense of celebration" in the early hours of Monday as it opened to midnight customers.
"I'm hoping that this is a sort of rebirth, and that we are reopen for the foreseeable," he said.
Marika Smith, general manager of Hough End Leisure Centre, Withington, Manchester, said all of their swimming times were already fully booked on Monday.
Kelly Boad, owner of the Hair & Beauty Gallery in Warwick, opened her salon at midnight for a symbolic "first cut" of 2021, adding she is fully booked for the first few weeks.
Another business that reopened at midnight in England was Secret Spa, which offers at-home salon and spa treatments in London, Manchester and Brighton.
Co-owner Emily Ewart-Perks said it had "been such a long time coming", saying: "Everyone has really missed the social contact of the day-to-day job and making clients happy."
She said they have experienced a "surge of bookings", including "a lot of 6am haircuts".
As of 10:00 BST, High Street footfall had more than trebled from a week earlier, as queues formed outside branches of Primark, JD Sports and TK Maxx and retailers extended their opening hours.
The rule changes in England from Monday include:
- All shops can reopen
- Hairdressers, beauty salons and other close-contact services can open
- Restaurants and pubs are allowed to serve food and alcohol to customers sitting outdoors
- Gyms, spas, zoos, theme parks, libraries and community centres can all open
- Members of the same household can take a holiday in England in self-contained accommodation
- Non-essential journeys between England and Wales are allowed
- Up to 15 people can attend weddings and 30 can attend funerals
- Children can attend any indoor children's activity
- Care home visitors will increase to two per resident
- Driving lessons can resume, with tests restarting on 22 April
But the British Beer and Pub Association has estimated that only 40% of licensed premises have the space to reopen for outdoor service.
In Northern Ireland, the remaining school year groups 8-11 will return to the classroom. The stay-at-home message is being relaxed and up to 10 people from two households can meet in a private garden.
In Scotland, pupils at schools in six council areas go back to school today. Not everyone is returning on Monday because differing term times mean some schools are still closed for the Easter holidays.
After a drop in Covid cases prompted the Welsh Government to bring forward some dates for reopening, all students will return to face-to-face teaching on Monday.
Non-essential shops can also reopen, close-contact services can resume, driving lessons can restart and travel in and out of Wales from the rest of the UK is allowed.
https://www.bbc.com/news/uk-56710858
