Live updates: follow the latest news on Covid-19 variant Omicron
UK Prime Minister Boris Johnson has resisted introducing further restrictions in England before Christmas despite the spread of the Omicron variant, but warned that the situation "remains finely balanced".
He said measures after Christmas were still a possibility, urging people to be cautious and to take a Covid test before visiting elderly or vulnerable relatives.
“So what I can say tonight is that naturally we can’t rule out any further measures after Christmas – and we’re going to keep a constant eye on the data, and we’ll do whatever it takes to protect public health.
“But in view of the continuing uncertainty about several things – the severity of Omicron, uncertainty about the hospitalisation rate or the impact of the vaccine rollout or the boosters, we don’t think today that there is enough evidence to justify any tougher measures before Christmas.
“We continue to monitor Omicron very closely and if the situation deteriorates we will be ready to take action if needed. What this means is that people can go ahead with their Christmas plans but the situation remains finely balanced and I would urge everyone to exercise caution, to keep protecting yourselves and your loved ones, especially the vulnerable."
The Scottish government, meanwhile, has cancelled Edinburgh's Hogmanay street party and drastically limited the numbers of spectators allowed at events to counter the rapid spread of the Omicron variant.
People have also been urged to limit their socialising over the New Year period as part of measures that First Minister Nicola Sturgeon thought were required to slow the spread of Covid-19.
Outdoor events, including the derby between Glasgow football clubs Celtic and Rangers, will be limited to 500 people. Indoor events will be restricted to 200 people if seated or 100 if standing.
“Difficult though it is, please follow this advice over New Year – minimise Hogmanay socialising as much as you can,” Ms Sturgeon said.
“If we all follow the advice to minimise the contact we have outside our own households, we will help limit the spread of infections.
“This is the bedrock of our plan for the immediate period ahead.”
The measures will come into force on December 26, and continue for at least three weeks.
“This will, of course, make sports matches, including football, effectively spectator-free over this three-week period,” said Ms Sturgeon.
“And it will also mean that large-scale Hogmanay celebrations, including that planned here in our capital city, will not proceed.
“I know how disappointing this will be for those looking forward to these events, and for the organisers of them.”
It follows similar measures in Wales that will force indoor and outdoor events to be held behind closed doors from Boxing Day.
On Tuesday, the UK reported 90,629 new Covid-19 cases, with total infections in the past seven days 63 per cent higher than the previous week.
Chancellor Rishi Sunak has introduced a £1 billion ($1.33bn) support package for businesses to cope with the impact of Omicron. That includes one-off grants of up to £6,000 for firms affected and the government covering sick pay for Covid-related absences for small and medium-sized businesses.
Jeremy Farrar, a medical researcher and director of charitable foundation Wellcome Trust, said Omicron "is spreading unbelievably fast".
"It is a phenomenal variant, transmission is eye-wateringly high, but there is great uncertainty," he told the BBC.