With Christmas fast approaching, there are concerns about how relaxing restrictions and allowing households to meet over the festive period could impact coronavirus infection rates.
It comes as millions of people in England face the harshest local Covid restrictions after an exponential surge in cases.
Both Wales and Northern Ireland have already announced they will enter new lockdowns after Christmas.
So could England and Scotland face the toughest restrictions again in January? Here’s everything you need to know.
Will there be another lockdown?
A third lockdown in England could be possible, after Downing Street refused to rule out putting the country back under blanket restrictions after Christmas.
When asked whether a third lockdown was possible, Boris Johnson’s official spokesman said while the plan is for the tiered approach to be implemented until spring, “the latest data” would be kept under review.
He said: “As we said at the time of publishing the winter Covid Plan, we’ve been clear of the rationale behind the tiered regional approach and that’s what we set out at the time.
“We’ve obviously updated them today - that is designed to reduce the rate of transmission and reduce the R rate in areas where there is high prevalence.
“But as we’ve said throughout, we will obviously keep the latest data and latest trends under review. That has been the case throughout.
“But as I say, the winter Covid Plan sets out the path to Spring and that is focused around the regionalised tiered approach.”
In Scotland, Deputy First Minister John Swinney has warned that a potential lockdown after Christmas cannot be ruled out.
The Scottish Government has also confirmed that areas in Scotland could face stricter local lockdown measures when the five-tier system is reviewed on Tuesday 22 December, the final review before Christmas.
When asked, Mr Swinney did not rule out the idea of another lockdown or harsher restrictions, saying it could be a “possibility”.
He said: "We'll have to look at what the forward prospects look like, we'll have to take decisions that will be sustainable for a period into January and February to protect the public interest and protect the National Health Service.”
And Professor John Edmunds, a member of the scientific advisory group Sage, told Sky News on 18 December that measures are likely to have to be tightened after Christmas.
He said: “At the moment it doesn’t look like the tier system is holding the epidemic wave back, unfortunately.
“So I think we are going to have to look at these measures and perhaps tighten them up, we really will. It’s a horrible thing to have to say but we are in quite a difficult position.”
Are any of the other UK nations facing another lockdown?
While England and Scotland will keep with their different tier systems for now, other UK nations have announced further lockdowns to curb the spread of the virus.
Wales has said its third national lockdown - otherwise known as Alert Level 4 - will commence straight after the Christmas bubbles period ends, from 28 December.
The country’s First Minister said the lockdown will be reviewed after three weeks, but it has no end date.
A Welsh Government spokesperson said: “Level 4 restrictions will come into force at 6pm on 25 December, but there will be exceptions for the Christmas period that will remain (the 2 household bubble, travel to or from your Christmas bubble and accommodation open).
"These Christmas exceptions will then lapse for most people by the end of the day on the 27 – and by the end of the day on the 28, for people travelling to/from Northern Ireland.
"We will be fully in Level 4 by the end of the day on 28 December.”
Northern Ireland has also decided to enforce another lockdown, beginning on Boxing Day and lasting for six weeks.
People will still be able to form Christmas bubbles, but anyone visiting another household must leave by 28 December.
The measures in the nation will be similar to the “sustained” lockdown which was implemented back in March.
All non-essential retail services will close, including beauty salons. Pubs, cafes and restaurants will be restricted to take away services only.
Could the relaxed Christmas rules lead to rising cases?
Boris Johnson announced that the four nations had “unanimously” decided not to change the relaxed Christmas rules, which allow up to three households to meet indoors between 23 to 27 December.
All four nations will go ahead with the plans, although leaders have given out tougher warnings about the risks of meeting up with others over those days.
The Prime Minister urged people to keep their celebrations as small as possible, saying: "A smaller Christmas is a safe Christmas”.
And First Minister Nicola Sturgeon advised Scots on Wednesday 16 December that the safest way to spend Christmas was to stay within their own households and homes.
Wales is the only country which has diverged from the UK-wide plan by reducing the number of households allowed to meet from three to two.
However, the Chief Executive of the Royal College of Nursing, Dame Donna Kinnair, said people visiting loved ones at Christmas would “undoubtedly” lead to more virus cases in 2021.
She said: “Travelling and family visits associated with this time of year will undoubtedly lead to more cases, more pressure on NHS and care services, and more deaths.
"By turning the second and third waves into an unrelenting tsunami, we would begin 2021 in the worst possible way."