Boris Johnson did not rule out the potential return of COVID restrictions in the future on Monday as he announced plans for "freedom day" on 19 July.
Speaking at a Downing Street press conference, the prime minister set out his plans to move England into step four of his unlocking roadmap. The final decision on whether or not that happens on the planned date will be taken a week earlier, on 12 July.
Johnson has repeatedly said he hopes the roadmap will be “irreversible” as the vaccine programme continues to keep deaths and serious illness numbers down.
But as the PM closed his speech on Monday, he said the government would continue to monitor the data and “retain contingency measures”.
If a new variant of coronavirus emerges that is resistant to the vaccine, the government would have to take steps to keep the public safe, he said.
“We will continue to monitor the data and retain contingency measures to help manage the virus during higher-risk periods such as the winter," he said.
“But we will place an emphasis on strengthened guidance and do everything possible to avoid reimposing restrictions with all the costs that they bring.”
Johnson also said the virus will have an extra advantage in the upcoming colder months.
The Scientific Advisory Group for Emergencies (Sage) has already warned that transmission will increase in autumn and winter.
This could mean the effectiveness of baseline measures varies through the year and would have to be augmented to have the same impact.
On the prospect of reintroducing measures, the PM said: “It is very far from the end of dealing with this virus.
“On the irreversibility point, obviously, if we do find another variant that doesn’t respond to the vaccines, if heaven forbid if some really awful new bug appears, then clearly we will have to take any step we need to do to protect the public.”
Watch: Boris Johnson sets out step four changes to COVID lockdown roadmap
It comes despite the Delta variant, which first originated in India, having recently driven up case and death numbers in the UK.
Officials have acknowledged infections will continue to increase – albeit at a much lower level than before the vaccination programme.
But Johnson said it has now become necessary to find a new way to live with the virus.
He said we must "balance the risk" of disease from the virus with the harm from continuing with legal restrictions that "inevitably take their toll on people's lives and livelihoods, on people's health and mental health".
He added: "And we must be honest with ourselves that if we can't reopen our society in the next few weeks when we will be helped by the arrival of summer, and by the school holidays, then we must ask ourselves, 'when will we be able to return to normal?'.
"And to those who say we should delay again – the alternative to that is to open up in winter when the virus will have an advantage, or not at all this year."
Under step four of the roadmap, Johnson announced there would be no limits on social contact, meaning the end of orders such as the “rule of six” and restrictions on guests at weddings.
The legal requirement to wear face coverings would also be lifted, although guidance would suggest people might choose to do so in “enclosed and crowded places”, he said.
All remaining businesses would be able to reopen, including nightclubs with no caps on capacity while other hospitality venues would no longer be restricted to table service.
Finally, the “one metre plus” rule on social distancing would be lifted except in specific circumstances such as at the border, where guidance would remain to keep passengers from red and amber list countries from mingling with other travellers.
Watch: PM confirms face masks to become 'personal choice'