Boris Johnson is preparing to replace the "rule of six" with tougher restrictions on daily life as he warned that Britain is in the grip of a second wave of coronavirus.
The Prime Minister said he might have to "intensify" measures that could act as a temporary "circuit break" to stem a resurgence of the virus and prevent Britain being forced into a second lockdown.
Johnson was to spend the weekend in Downing Street with officials considering options including closing pubs and restaurants or imposing 10pm curfews and a nationwide ban on friends and separate households socialising.
Schools would only be closed as a "last resort", Whitehall sources said.
The two-week "circuit break" shutdown could be announced in a televised press conference as early as Tuesday.
The developments come as daily coronavirus infections surged to a four-month high of 4322 and data suggested that hospital admissions would be heading back to mid-March levels by next weekend.
Health chiefs on Friday put the temporary Nightingale Hospital in Birmingham's NEC on standby so it could start treating patients within two to three days.
Curbs including a curfew on pubs and restaurants and a ban on socialising outside of households were also announced across parts of the North West, the Midlands and West Yorkshire from Tuesday.
It means around 13 million people now face local restrictions.
Industry chiefs warned that further measures could cost thousands of jobs. Kate Nicholls, the chief executive of UK Hospitality, said: "We've still got one million people in hospitality whose jobs are in part or in full supported by furlough, which ends in October.
"If we can't bring those people back now, then we will struggle to bring those jobs back after a circuit break."
Hannah Essex, the co-director of the British Chambers of Commerce, urged the Government to "do everything in its power to avoid further national lockdowns that will cripple business".
"Any new restrictions must be accompanied by a comprehensive support package for the hardest-hit firms forced to close or reduce capacity through no fault of their own," she said.
Speaking during a visit to Oxfordshire, Johnson said: "Clearly, when you look at what is happening, you've got to wonder if we need to go further than the 'rule of six'.
"So we'll be looking at the local lockdowns we've got in large parts of the country now. We'll be looking at what we can do to intensify things there, to help bring the rate of infection down there, but also looking at other measures as well. We are now seeing a second wave coming in.
"I don't want to go into a second national lockdown at all. That's the last thing anybody wants. I don't want to go into a bigger lockdown measures at all. We want to keep schools open."
Government advisers are pressing for rapid action and are understood to have proposed the two-week period of national rules as the "circuit break" to stem the rise in coronavirus cases.
It had been thought it could be delayed to late October to coincide with schools' autumn half-term, but Public Health England said data published on Friday could be a sign of "far worse things to come" as the Office for National Statistics said cases had almost doubled in a week to 6000 a day in England – its worst assessment since mid-May (the graphic below shows where the rises are highest).
Treasury insiders signalled on Friday that a two-week "circuit break" would be "far better" than being forced into a full lockdown in several weeks time as a result of no further action being taken.
Another source added: "Over the weekend, there will be a lot of work to draw up measures, get the science and all the options out. What can we implement that doesn't tank the economy?"
Ministers are understood to be worried about the impact of the return of students to universities. On Friday, St Andrews became the first to urge a voluntary 7pm curfew on students to restrict socialising.
Susan Michie, professor of health psychology at UCL and a member of the Government's Scientific Advisory Group for Emergencies (Sage), warned ministers not to repeat the mistake of the March lockdown in implementing measures too slowly.
"We need a stitch in time. We need to learn the lessons of the spring," she said. "Every day's delay to a step change in measures to restrict transmission when it is increasing exponentially will be expensive in terms of health and lives in the short term and the economy in the long term."
Prof Michie proposed closing pubs, bars and restaurants, reducing the number of households meeting, a return to essential travel only, working at home if possible, online lectures at universities where possible and an extension of furlough until next year, as Germany has done.
Paul Hunter, professor of medicine at the University of East Anglia, warned that a two-week shutdown would not be long enough to undo the current damage, saying: "The problem is that cases decline in lockdown at a much slower rate than cases increase during the period before."
Nicola Sturgeon, Scotland's First Minister, said the country was at "probably the most critical point" since lockdown was imposed in March and disclosed that she had asked Johnson to convene a Cobra meeting for a UK-wide discussion.
And Sadiq Khan, the Mayor of London, warned that lockdown restrictions were "increasingly likely" in the capital after he held an emergency meeting with the Government and council leaders.