Britain could be locked down to force people into self-isolation "very soon", as the prime minister considers racing new laws through the Commons in a day to tackle the coronavirus pandemic.
MPs are returning to parliament after the weekend to debate the government's Coronavirus Bill in all its stages, before it goes to the House of Lords and becomes law by the end of this week.
The Commons debate follows a stark warning from the prime minister that the UK is heading towards a lockdown, after appeals to the public to stay indoors were largely ignored during a sunny Mother's Day.
At his latest Downing Street news conference, Mr Johnson said further measures would be considered in the next 24 hours to prevent the spread of COVID-19 if people fail to stay two metres apart.
He admitted being outdoors was "crucial for health, physical and mental well-being", but warned people not to think that "fresh air in itself automatically provides some immunity".
Health Secretary Matt Hancock told Sky News' Kay Burley@Breakfast on Monday: "We will enforce and bring in further strong measures if we need to - but I'd much rather people follow the rules themselves, it would be much more straight forward."
"If we need to go further in terms of people's interactions then we will."
He added those decisions would be made "very soon".
Ahead of the Commons debate, the government has also responded to a backlash against wealthy families fleeing towns and cities for holiday homes by attempting to stop them from travelling.
Updating guidance on non-essential travel, the government has now declared: "Essential travel does not include visits to second homes, camp sites, caravan parks or similar, whether for isolation purposes or holidays.
"People should remain in their primary residence. Not taking these steps puts additional pressure on communities and services that are already at risk."
In other moves in the government's war against the virus, 1.5 million letters are being sent to elderly and vulnerable people ordering them to stay at home as part of a so-called "shielding" process.
And as the UK lurches towards a lockdown, more high street stores are not opening, fast food chain McDonald's is shutting its restaurants at 7pm and many local authorities are closing parks and open spaces.
A person at an old peoples' home in Primrose Hill, north London, was pictured being carried out on a stretcher by medics wearing protective clothing.
The Coronavirus Bill, which runs to more than 320 pages, contains:
The bill proposes that police, public health and immigration officers will be able to detain people suspected of having COVID-19 and exact fines of up to £1,000 for refusing to submit to a test.
Other powers in the bill include registering retired doctors or medical students, having video links in courts, banning public events and new rules for supermarkets on food supplies.
The bill states: "We assume the vast majority of people will comply with relevant public health advice. The policy aim of these provisions is to ensure that proportionate measures can be enforced if and when necessary.
"The proposals will provide public health officers, constables and (in some circumstances) immigration officers with the means to enforce sensible public health restrictions, including returning people to places that they have been required to stay."
But while the opposition parties have promised to co-operate with the government in enabling the legislation to become law speedily, Labour claimed after a weekend of "public confusion and widespread non-compliance" with social distancing that "something has to change".
"We now call on the government to move to enforced social distancing and greater social protection as a matter of urgency," said shadow health secretary Jon Ashworth.
There is also alarm in all parties over keeping the emergency legislation operating for two years.
Veteran Labour MP Harriet Harman, who chairs parliament's human rights committee, has teamed up with former Tory cabinet ministers David Davis and Andrew Mitchell and the SNP's Joanna Cherry to limit the emergency powers to six or 12 months.
Downing Street has responded by offering to insert a review every six months and a vote in the Commons.
Scottish First Minister Nicola Sturgeon has told shops currently not obliged to shut that if they are not providing medicine or food they should close.
Irish Prime Minister Leo Varadkar suggested a tighter lockdown could also come into force in his country.
He thought scenes similar to those in the UK of large groups of people ignoring social distancing advice and heading to public places was probably explained by people not realising how busy it would be.
"I don't think we should be berating people about this," he said.
Mr Varadkar added Ireland's chief medical officer was looking at if a bigger lockdown is needed, commenting: "If they recommend further restrictions, we will implement further restrictions."