All Covid restrictions will end in England on Thursday and free mass testing will stop from 1 April.
The prime minister told MPs the legal duty to isolate for those who tested positive would be dropped as he unveiled his "living with Covid" plan.
From 1 April the provision of free testing would be targeted to the most vulnerable, Boris Johnson said.
But the British Medical Association, a doctors' union, said the plan failed to protect those most at risk from Covid.
And opposition parties said the prime minister's blueprint out of the pandemic had moved too fast, and voiced concern over the scaling back of free testing.
The Scottish government said the public health advice it had received did not recommend lifting the restrictions.
Speaking at a Downing Street news conference on Monday evening, Mr Johnson said "today is not the day we can declare victory over Covid because this virus is not going away".
He described the pandemic as "two of the darkest, grimmest years in our peacetime history".
However, he said the nation had passed the peak of Omicron, with falling cases and hospital admissions.
And he said the country could now complete the "transition back towards normality" while retaining contingencies to respond to a Covid resurgence or a new variant.
England's chief medical officer Prof Sir Chris Whitty said the ending of virus restrictions was a "gradual, steady change over a period of time", adding: "This is not a sudden 'everything stops'."
He said the number of people being infected with Omicron was still "very high".
Office for National Statistics (ONS) infection figures last week estimated that one in 20 people in England had Covid.
Sir Chris said the public health advice for people with Covid would still be to self-isolate to prevent others catching it, as it would be for many other highly infectious diseases.
Sir Patrick Vallance, the UK government's chief scientific adviser, warned the virus would continue to evolve over the next couple of years and there was no guarantee that future variants would be less severe than Omicron.
He argued it was crucial the nation retained a virus surveillance system to monitor new threats and the capacity to "ramp up" measures again quickly to protect the vulnerable.
What is changing in England?
From 21 February: the government is dropping guidance for staff and students in most education and childcare settings to undertake twice weekly asymptomatic testing
From Thursday 24 February:
- People who test positive for Covid will no longer be legally required to self-isolate
- But they will still be advised to stay at home and avoid contact with others for at least five full days
- Routine contact tracing will end, so fully-vaccinated close contacts and those under 18 will no longer be legally required to test daily for seven days
- The £500 self-isolation support payment for people on low incomes who test positive for Covid will no longer be available
- Covid provisions for increased statutory sick pay will apply for a further month
From 1 April:
- Free mass symptomatic and asymptomatic testing for the general public will end, and will instead be targeted towards the most vulnerable
- People with Covid symptoms will be asked to exercise personal responsibility when deciding whether to stay at home - until then they are still advised to do so
- Current government guidance on Covid passports will end and it will no longer recommend venues use the NHS Covid pass
Earlier, Mr Johnson told MPs it was time to move from government restrictions to people exercising personal responsibility.
It was only because levels of immunity were so high and deaths were now "below where you would normally expect for this time of year" that the government could lift the restrictions, he said.
As Omicron was less severe, testing for it "on the colossal scale we've been doing" was less important and less valuable in preventing serious illness, he added.
Limited free lateral flow tests for the most vulnerable groups would still be provided, the PM said, and ministers would work with retailers to ensure everyone who wanted a test could buy one.
The PM did not specify which groups of people would be deemed "most vulnerable".
To prevent the stockpiling of free lateral flow tests before 1 April, people will only be able to order a box of tests every three days instead of every 24 hours.
Once tests are no longer free, ministers expect a market for lateral flow tests to develop, with individual tests expected to cost a few pounds.
The scaling back of testing comes after Mr Johnson previously told the BBC £2bn had been spent on the testing system in January alone.
Mr Johnson said "targeted vaccines and treatments" would be in place for the most vulnerable, and the government would follow the recommendation of the UK's vaccine advisory body to offer an additional booster jab to the over-75s and the most vulnerable over-12s this spring.
He added the government would maintain its resilience to respond to resurgences from the virus, including by keeping the Office for National Statistics infection surveillance survey to keep track of surges when they happen.
'An axe to testing'
Ministers have taken an axe to testing - going further than many experts thought they should.
A number had called for rapid lateral flow tests to be made available to older people, and those with health conditions, so they could get family and friends to use them before visiting.
Instead, beyond social care staff, only those deemed at-risk will get access to tests in the community - and only then if they have symptoms.
The at-risk group has not been defined, but is likely to be the most vulnerable who would benefit from antiviral treatments to reduce the risk of them needing hospital admission. This includes the severely immuno-compromised. A healthy 80-year-old would not qualify.
These changes will come in on 1 April and by that stage infection levels could be at very low rates. The scaling back may not seem that significant if that is the case.
But the big caveat is that the government will retain the ability to ramp testing back up if the circumstances demand it - either because infection rates take a turn for a worse, or a new variant emerges.
Mr Johnson also promised that the UK government would continue to work with the devolved administrations of Scotland, Wales and Northern Ireland as they decided how to take forward their own plans.
But Scottish health secretary Humza Yousaf said free tests and self-isolating when positive with Covid were effective tools in suppressing the virus and said the public health advice the Scottish government had received "does not advise removing these important interventions at this time".
He called for the UK government to continue supplying "adequate" funding for all parts of the UK to do what they deemed necessary to tackle the virus.
Northern Ireland's health minister Robin Swann said his department would "carefully consider" England's plan, but no decisions had been made on changes to his country's test and trace programme.
Labour leader Sir Keir Starmer described the PM's plan as a "half-baked announcement from a government paralysed by chaos and incompetence".
He said the PM's strategy was not "a plan to live well with Covid" and would instead "leave us vulnerable".
Dr Chaand Nagpaul, council chairman of the BMA, said the strategy neglected some of society's most vulnerable and instead of giving people more freedom, it was likely to cause "more uncertainty and anxiety".
"Living with Covid-19 must not mean ignoring the virus all together - which in many respects the government's plan in England seems to do," he said.
Dr Nagpaul called for "urgent clarity" on testing for NHS workers to protect staff and patients and that "protections must be maintained for the most vulnerable, including the provision of enhanced face masks, and clear guidance for both patients and clinicians".
Chris Hopson, chief executive of NHS Providers which represents hospital trusts, said many NHS figures were "concerned about the potential impact of these decisions" and it was "vital" the government was ready to restore phased out testing and surveillance systems should they be needed.
Ministers should assess the impact of restricting access to free testing, he said, warning there was a risk of "significantly exacerbating health inequalities".
The Blood Cancer UK charity accused the government of lifting restrictions "without a plan to protect immunocompromised people" and warned the move would leave many of them "feeling abandoned". It said that of the 500,000 severely immunocompromised people in the UK, about 230,000 have blood cancer.
Plan B measures - introduced in December to stem the spread of the Omicron variant - including the requirement to wear masks in public places and the use of Covid passes for large events, were abolished in England last month.
Face masks continue to be a condition of carriage on London's transport network, but London mayor Sadiq Khan said on Monday that he expected the rules would be lifted following the PM's announcement.
Just over 91% of people in the UK aged 12 and over have had a first dose of a vaccine, 85% a second jab, and 66% a booster or a third dose, according to official data.
On Monday, the UK recorded a further 38,409 confirmed daily cases and another 15 deaths within 28 days of a positive Covid test.