London is under new tier-4 Covid restrictions from Sunday (December 20), following the emergence of a faster-spreading coronavirus variant.

Boris Johnson has cancelled Christmas get-togethers for millions of people across London and south-east England.

If you are in tier 4 you cannot meet other people indoors, including over the Christmas period, unless you live with them, or they are part of your existing support bubble.

Outdoors, you can only meet one person from another household.

Non-essential retail, indoor gyms and leisure facilities in these areas will close.

People have been told not to travel out of tier 4, other than for permitted reasons such as work that cannot be done at home, education, health or meeting someone in your support bubble.

In tiers 1 to 3 in England, the Christmas relaxation allowing a maximum of three households to mix will be restricted to Christmas Day only.

The Prime Minister said: “I know how much emotion people invest in this time of year, and how important it is, for instance, for grandparents to see their grandchildren, for families to be together.

“So I know how disappointing this will be.

“But we have said throughout this pandemic that we must and we will be guided by the science.

“When the science changes, we must change our response.”

A further 339 people who tested positive for coronavirus have died in hospital in England, bringing the total number of confirmed deaths reported in hospitals to 46,122, NHS England said on Saturday.

Commenting on changes to Christmas rules, Mr Johnson said that as prime minster he believed there was “no alternative open to me”.

He said: “Without action the evidence suggests that infections would soar, hospitals would become overwhelmed and many thousands more would lose their lives.”

All restrictions will be reviewed on December 30.

Labour leader and Holbron and St Pancras MP Sir Keir Starmer tweeted: "Millions will be heartbroken by this news, having their Christmas plans ripped up with less than a week’s notice. At this time of national crisis, the British people want clear, decisive leadership. All we get from Boris Johnson is confusion and indecision."

Shadow minister for mental health Dr Rosena Allin-Khan said: “Christmas plans are ruined for families up and down the country because of government neglect, incompetence and an inability to get on top of this virus.

“Dither and delay has cost lives with more to come. The mental health implications of this will be tragic.

“The new strain isn’t solely to blame here. Boris Johnson must be held to account over this: Barnard Castle/Cummings; second lockdown came too late; terribly confused rules; “back to normal by Christmas” messaging; failing test and trace.

"Serial mismanagement. National negligence.”

Mayor of London Sadiq Khan said: “These further restrictions are a bitter blow for Londoners who were hoping to spend time with loved ones safely this Christmas, and for businesses who have already suffered so much this year.

“London faces its toughest Christmas since the war and the whole city will need to pull together to see us through this terrible period.

“Implementing restrictions is not enough – it is imperative that the Government vastly increase mass testing as a matter of urgency.

“Providing greater financial support to businesses and the self-employed, currently woefully insufficient, is crucial.

“The government needs to put in place a compensation scheme for all lost income for the festive period, as well as a package of full pay for those who are required to self-isolate.

“Face coverings should be made mandatory in all busy outdoor public places.

“London and the country are paying the price for the Government’s continued failure to get a handle on the pandemic. This continued chaos and confusion could all have been avoided had the Government not made irresponsible promises to the public and raised expectations about the Christmas period.

“I urge Londoners to follow the new restrictions very closely, so that we can protect our NHS and prevent more tragic deaths.

“It would be such a tragedy to lose even more people to this disease when the vaccine is now being rolled out across our city and those lives could be saved.”

Sir Patrick Vallance said that three questions needed to be asked about the new variant of coronavirus; whether it could be transmitted more readily, whether it made people sicker, and whether it altered the immune response caused by vaccines.

He said the variant, which was thought to have emerged in mid-September in London or Kent, had a “significant substantial increase in transmissibility”.

Sir Patrick added that by December over 60% of infections in the capital had been the new variant, saying: “It moves fast and is becoming the dominant variant.”

Helen Dickinson, chief executive of the British Retail Consortium, said: “We recognise that the government has difficult decisions to make and the situation with the pandemic is very fast moving, but this is hugely regrettable news.

“Retailers have invested hundreds of millions of pounds making stores Covid-secure for customers and staff, and Sage’s advice has said throughout that closing non-essential retail has a minimal impact on the spread of the virus.

“The consequences of this decision will be severe. For businesses, the government’s stop-start approach is deeply unhelpful – this decision comes only two weeks after the end of the last national lockdown and right in the middle of peak trading which so many are depending on to power their recovery.

“Faced with this news – and the prospect of losing £2 billion per week in sales for the third time this year – many businesses will be in serious difficulty and many thousands of jobs could be at risk.

“The government will need to offer additional financial support to help these businesses get back on an even keel – an extension to business rates relief in 2021 is the best place to start.”