However, some scientists argue that the spread of the virus will continue to accelerate even if the whole of the country was placed under this “Stay at Home” level.
The prime minister has not ruled out a third national lockdown but a government source told the Mirror that ministers could simply add "another level on to tier 4, so like a tier 5".
What would tier 5 involve?
One of the main differences between tier 4 and the first national lockdown is that schools, universities and places of worship can remain open.
Experts and teaching unions have already called on the government to delay the start of the new term in January and a study by scientists at the London School of the London School of Hygiene and Tropical Medicine warned that the R number would not fall below one "unless primary schools, secondary schools, and universities are also closed."
The government has said it is "still planning for a staggered opening of schools" but is keeping the approach under constant review.
Susan Michie, professor of health psychology at University College London, told the Independent that the government should work with teachers, unions and parents to ensure all children were taught online in January.
“Unfortunately, because of the evidence we do have about the contribution of schools to the R level, shutting schools for January is wise – but only if the government takes that time to ensure schools are safe,” she said.
“What we need is a plan so that all children have digital access so that whether schools go back or not everyone can learn at home. We could bring back as many retired schoolteachers as possible to help with online learning, for example. Otherwise this will just go on longer and longer.”
Other suggestions for tier 5 include banning people from leaving their homes for non-essential reasons, matching the restrictions at the outbreak of the pandemic. This meant people could only go out for to get food and urgent supplies, to provide care or for daily exercise.
Weddings and funeral services, which can currently take place with restricted numbers, could also be banned. Sports facilities such as golf courses and tennis courts could be closed as in the second lockdown.
Another option is to further restrict domestic and international travel.
Some experts believe that national restrictions are now needed given the recent increase in transmission, with over 40,000 new infections recorded for the first in the UK on Monday.
Stephen Reicher, a Sage member and Professor of Social Psychology at the University of St Andrews, highlighted that modelling suggested current tier 4 measures would not bring R down to below 1.
He told the Independent: “We need something more and we need it to be national (given the new variant is now spread nationally) and we need it now. We are in a real emergency. We need an emergency response.”
Professor Michie told the Independent that another lockdown was inevitable and that it was "just a question of when”. She added: "I don't know what there would be open under tier 5 that wouldn't be open under lockdown.
“We could have the same measures but call it tier 5, because we do know that the first lockdown worked. This virus is now 57 per cent more infectious, this is a new pandemic we are dealing with, so to have anything less this time around does not seem sensible."
Andrew Hayward, who sits on the government’s New and Emerging Respiratory Virus Threats Advisory Group (Nervtag), told BBC Radio 4 that national action was needed “to prevent a catastrophe in January and February”.
“I think we’re really looking at a situation where we’re moving into near lockdown," he added. But I think what we need to remember is that whilst lockdowns work they only really work if you can afford to lockdown. We need to be able to make people who can’t afford to protect themselves and contribute to control to be able to do that."
On Tuesday, the UK reported more than 53,000 new cases of coronavirus - the highest daily figure since the pandemic began. The day before, around 40,000 new cases were reported, which was a new single-day record at the time.
Dr Susan Hopkins, senior medical adviser for Public Health England (PHE), said the "unprecedented levels" of Covid-19 infection across the UK was of "extreme concern".
"Whilst the number of cases reported today include some from over the festive period, these figures are largely a reflection of a real increase," she said on Tuesday.
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