The government is facing calls from Tory backbenchers to drop the 2m (6ft) social distancing rule in England.
MPs, including former cabinet ministers Sir Iain Duncan Smith and Damian Green, say it is essential for the economy.
The government has said it is constantly reviewing its coronavirus lockdown guidance.
It follows the announcement of a further easing of restrictions in England, allowing single adults to stay at one other household from Saturday.
No 10 said the change aimed to help combat loneliness and that people were being trusted to observe the rules.
The relaxation does not apply to those who are shielding, or other UK nations.
Latest government figures show a further 151 people with coronavirus have died in the UK, across all settings, taking the country's death toll to 41,279.
Meanwhile, Labour leader Sir Keir Starmer has accused ministers of "mismanagement" over the reopening of schools, saying the government is putting the welfare and education of children at risk.
As the lockdown continues to be eased in England, there are fears in Westminster and the business community that keeping the 2m rule will significantly impede economic recovery.
Former Conservative Party leader Sir Iain warned of dire economic consequences, with public transport running quieter than necessary and pubs, restaurants and cafes unable to stage a proper recovery or even open.
He has urged ministers to move to a 1m policy - in line with World Health Organization guidance already followed by countries including France, Denmark and Singapore.
Sir Iain described the 2m rule as "the critical component around which everything coming out of lockdown hinges".
"Our economy is facing a complete crash: the debts we're racking up on how we're supporting people, the fact no work or very little work is taking place," he said.
"If we don't get the economy moving, we will be unable to afford any of the things that we need to support public services, so getting the balance right is important."
A decision over the 2m rule looms
This is a very tricky moment for the prime minister.
More and more MPs believe that relaxing the 2m rule would be the crucial piece of the jigsaw.
And if 1m is deemed safe in Denmark, France, or Hong Kong, then why not here?
First off, the disease is shrinking, but it's not disappearing fast.
And the government's top medics have said publicly that they don't think the 2m rule should go.
To change it therefore would be to go against the advice.
Science is as full of dispute as politics, even though the methods and practices are chalk and cheese.
And ultimately the decisions about handling the crisis have been made by ministers after receiving the scientists' advice.
But the decision over 2m is looming and it's one that Boris Johnson can't ignore.
Mr Green told the BBC's Newsnight scrapping the 2m guidance was the "single biggest change" the government should make in the coming weeks.
"I think that makes a huge difference to many parts of industry, particularly hospitality businesses, restaurants, pubs, and so on," he told the programme.
"We've seen other countries do that, actually move from 2m to 1m, without any damaging effects so far."
Tory backbenchers made similar points to Chancellor Rishi Sunak - who admitted the rule made things difficult for opening up - behind closed doors on Wednesday night, according to BBC political correspondent Nick Eardley.
Greg Clark, chair of the Science and Technology Committee, who has previously called for the rule to be reconsidered, said: "The government should have the courage to change it, if the evidence recommends it."
Speaking on BBC Radio 4's Today programme, local government minister Simon Clarke said: "We all recognise how limiting 2m is. We're not blind to the very severe challenges this causes, not just for schools but for the wider economy."
But he said the "best available guidance" supported keeping the rule at the moment, adding: "We've heard from our scientists about that literally in the last 24 hours."
The prime minister's official spokesman said the rule was being "kept under constant review" but added that Boris Johnson "doesn't feel the incidence of disease is as low as he would like".
Sir Patrick Vallance, the UK's chief scientific adviser, told reporters: "It is a risk-based assessment on when risk reduces and the risks are associated with distance, so risk falls after 2m," he said.
"It is wrong to portray this as a scientific rule that says it is 2m or nothing - that is not what the advice has been and it is not what the advice is now," he added.
Meanwhile, more than 31,000 close contacts were identified during the first week of the test and trace system in England, figures show.
It comes amid continued debate over schools reopening in England, after it was confirmed most children would not return to classrooms until September.
Sir Keir urged the prime minister to act now to ensure that target could be met.
Writing in the Daily Telegraph, he said "creativity" was needed to utilise empty buildings, including theatres, museums and libraries, as makeshift classrooms.
Mr Johnson said there would be a national "catch-up programme" for pupils in England, but warned a September return date for all pupils would depend on whether progress continued to be made in controlling the virus.