Scientists have warned that the easing of coronavirus restrictions over Christmas will cause a spike in infections, as London and some surrounding areas prepare to enter Tier 3.

The capital and parts of the commuter belt will be placed under the toughest measures – forcing the closure of hospitality – from Wednesday following a “very sharp” rise in cases.

Health Secretary Matt Hancock said higher infections in the South East may be in part due to a newly identified variant of coronavirus which is growing faster than the existing one.

The discovery sparked fresh concerns over plans to allow up to three households to mix indoors from December 23 to 27 – with fears the country will “pay the price” in the new year.

David Nabarro, a World Health Organisation (WHO) special envoy working on Covid-19, said the price of such a relaxation “could well be very high”.

Urging people to think carefully about their plans, he told Times Radio: “Just ask yourself, is there any way in which you can perhaps not have the family get-togethers this year?

“It’s much better not to do it when there’s this kind of virus about.”

Professor Stephen Reicher, of the University of St Andrews, said: “Right now we are heading towards disaster.

“Given high levels of infection across the country and the increasing levels in some areas (such as London) it is inevitable that if we all do choose to meet up over Christmas then we will pay the price in the new year.”

The chief executive of the NHS Confederation, Danny Mortimer, questioned whether “these rules will be enough to protect the population in the short term”.

Tory former minister Stephen Hammond, who represents Wimbledon, told BBC Two’s Newsnight that he thought there would be a “rethinking” over whether it is appropriate for families to gather at Christmas.

Mr Hancock said people should be “extremely careful” about who they mix with in the run-up to Christmas if they are planning to see elderly relatives over the festive period.

England’s chief medical officer Chris Whitty also struck a cautious tone, saying people should not meet at Christmas just because they can.

He said: “The point of this (relaxation of rules) is for, under certain circumstances, families who wish to, to get together, but they really have to be very, very careful.

“And in particular, incredibly careful if they’re around people who are vulnerable, who are at very high risk of this virus.”

Downing Street insisted there were no plans to change the “Christmas bubble” policy despite the fears.

The decision to move London and parts of Essex and Hertfordshire into Tier 3 affects almost 10.8 million people and means 61% of England’s population will be under the toughest restrictions from Wednesday.

It will have a devastating impact on the capital’s nightlife, with theatres forced to shut and pubs and restaurants closed apart from takeaway and delivery services.

Warnings to avoid travel to Tier 3 areas will also deprive some of the UK’s busiest shopping centres of trade at a crucial time of year.

Mr Hancock acknowledged the measures would be a “blow” to people and businesses as he addressed a Downing Street press conference.

But he said: “We know from experience that the best thing to do in the face of this virus is to act fast, not to wait to see its growth continue – and we do not rule out further action.

“This rise in transmission, as well as this new variant of Covid. should be a warning to us all that even after such a difficult year, we must stay vigilant.”

The Health Secretary stressed there was nothing to suggest the variant was more likely to cause serious disease, and suggested the vaccine should still be effective.

It came as:

– A further 232 people had died within 28 days of testing positive for Covid-19 as of Monday, while there were a further 20,263 lab-confirmed cases of coronavirus in the UK.

– Education Secretary Gavin Williamson warned Greenwich council to keep schools open to all pupils or it would face legal action.

– Sir Jeremy Farrar, director of the Wellcome Trust, said it would take almost a year to vaccinate the entire UK population against Covid-19, even with no interruptions in vaccine supply.

– Pub giant Wetherspoon announced it would slash beer prices in areas of southern England going into Tier 3 restrictions to 99p per pint until last orders on Tuesday.

The Government faced criticism from sectors of the economy affected by the decision to move London into Tier 3, as well as some Conservative backbenchers.

Kate Nicholls, of trade body UKHospitality, said the move places an “unfair, illogical and disproportionate burden on hospitality businesses without effectively tackling Covid”.

The British Beer and Pub Association said 1,250 pubs in London which had remained open in Tier 2 would be forced to close.

And theatre impresario Sir Cameron Mackintosh said the Government’s decision was “devastating” and “smacks of panic”.

Tory MP and former chief whip Mark Harper, leader of the Covid Recovery Group of lockdown sceptics, said the move “shows that the current strategy to combat Covid isn’t working”.

Meanwhile, the latest findings from Imperial College London’s seventh React study suggested the prevalence of coronavirus rose in parts of England towards the end of the second national lockdown.

The prevalence in London rose from 98 per 10,000 people in mid-November to 121 per 10,000 by the beginning of this month, according to the research.