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 aims to help combat loneliness and that people are being trusted to observe the rules.
The relaxation does not apply to those who are shielding, or other UK nations.
Meanwhile, Labour leader Sir Keir Starmer has accused ministers of “mismanagement” over the reopening of schools, saying the government was putting at risk both the welfare and education of children.
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 recovery.
Former Conservative Party leader Sir Iain has 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.
“The number one and single most important priority to unlock the economy is getting the distance down to one metre,” Sir Iain told the Daily Mail.
“The hospitality sector simply can’t make a living at two metres.”
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 scientist’s advice.
But the decision over 2m is looming and it’s one that Boris Johnson can’t ignore.
Another former Conservative cabinet minister, 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 two metres to one metre, without any damaging effects so far.”
Mr Green added that he would like to see the move come as part of “a package of ways of making sure that we do get our economy, across the board, open as fast as possible”.
Tory backbenchers made similar points to Chancellor Rishi Sunak – who admitted the rule makes things difficult for opening up – behind closed doors on Wednesday night, according to BBC political correspondent Nick Eardley.
At Wednesday’s daily Downing Street briefing, Prime Minister Boris Johnson pledged to “keep that two metre rule under constant review”.
He said there was a “balance of risk” to be struck, but caution was needed at present.
“I think the issue for me is how far down we can get the incidents of the disease. It’s not down as low as I would like,” Mr Johnson said.
“My judgement at present is that we must proceed cautiously and I think that is shared by the overwhelming majority of the public.”
Sir Patrick Vallance, the UK’s chief scientific adviser, told reporters at the briefing the 2m advice was “not a scientific rule”.
“It is a risk based assessment on when risk reduces and the risks are associated with distance, so risk falls after 2m,” he said.
He added: “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.”
It comes amid continued debate over schools reopening in England, after it was confirmed most children will not return to classrooms until September.
Sir Keir has called on the prime minister to act now to not risk the new target of September.
Writing in the Daily Telegraph, Sir Keir said “creativity” was needed to utilise empty buildings across Britain, including theatres, museums and libraries, so they could be “repurposed” as makeshift classrooms to ensure schools can resume fully after the summer holidays.
At the briefing, Mr Johnson also announced a new national “catch-up programme” for school pupils in England, and said a return for all pupils in September depended on progress continuing in controlling the virus.
Under the changes to lockdown rules announced on Wednesday, single adults can spend the night at another house in a “support bubble”.