Boris Johnson warned a second wave of coronavirus could sweep the UK as he said his ability to ease restrictions, including the two-metre limit, depended on the public following lockdown rules.
The prime minister has come under increasing pressure from Tory MPs over the social distancing limit, which bars and restaurant owners warn could ruin the hospitality industry.
The World Health Organisation (WHO) recommends people stay at least one metre away from each other.
But cutting the two metre rule to one metre could double the risk of infection, according to a scientific study published earlier this week.
Appearing at the daily Downing Street press conference, where Mr Johnson said he “would like” to reduce the limit.
But he warned any further lifting of restrictions depended on the public obeying simple rules - including the new duty set out by ministers on Tuesday that those with coronavirus symptoms must get a test.
And Sir Patrick Vallance, the government’s chief scientific adviser, cautioned that the UK was “not out of this yet.”
Mr Johnson warned there could be a second wave of Covid-19, a “kind of kinetic pulse of disease sweeping across the world”.
The risk of a second peak, which could again place the NHS under extreme pressure, was “all the more reason” to abide by the current lockdown measures designed to halt the spread of the disease, he said.
In a message to the millions watching at home, he said: “We want to take some more steps to unlock our society, and try to get back to as normal as possible. Eventually I would like to do such things as reducing the two metre rule for instance. But all those changes, all that future progress, depends entirely on our ability to keep.. and driving down the disease, and that depends on us following basic rules - wash your hands, self-isolate, if you have symptoms take a test, and observe social distancing”.
“We will beat this disease together, if everybody works on it together,” he added.
He also called on the public to resist the urge to meet friends indoors, as many parts of the UK brace themselves for wetter weather.
On Monday people in England were allowed to meet in groups of up to six for the first time since March, as long as they stayed outdoors.
Experts warn the disease is much more likely to spread indoors than outside.
Mr Johnson said he understood many people might be tempted to move the gatherings they have been enjoying outdoors indoors out of the rain.
“I really urge you: don't do that,” he said..
"We relaxed the rules on meeting outside for a very specific reason because the evidence shows the risks of transmission are much lower outdoors.”
He added: "Breaking these rules now could undermine and reverse all the progress that we've made together.
Sir Patrick also expressed fears the UK could face a second wave of Covid-19.
There were examples internationally of new outbreaks of coronavirus, he said, including in South Korea and parts of Germany as measures designed to inhibit the spread of the disease have been relaxed, he said.
There was a risk a second peak could come as a wave that travelled across the world, he added.
Earlier a YouGov poll suggested that a fifth of Britons are following lockdown rules less strictly than they were before, with a third citing Dominic Cummings as a factor.
The prime minister’s special adviser remains in post despite apparently breaching the rules by taking a 30 mile drive in county Durham while the rest of the country was being told to stay at home.