Boris Johnson has refused to back new Covid rules "for now" but warned the Omicron surge meant ministers can "rule nothing out" in the coming days.
The Prime Minister said the number of hospitalisations was "rising steeply" in some parts of the country and ministers "will have to reserve the possibility of taking further action" in order to "protect public health".
It comes as fears of a firebreak post-Christmas lockdown mount and after the Department for Health confirmed a further 91,743 Covid cases today.
After a meeting of the Cabinet, he said the arguments for taking action in the face of the spread of the new variant were “very, very finely balanced”.
“We have got cases of Omicron surging across the country now," he said. "We have got hospital admissions rising quite steeply in London and the obvious conclusion is that it was right to go fast with Plan B in the way that we did and also right to double the speed of the booster rollout,” he said.
“In view of the balance of risks and uncertainties, particularly around the infection, hospitalisation rate of Omicron – how many people does Omicron put in hospital – and some other uncertainties to do with the severity, the effectiveness and so on we agreed that we should keep the data from now on under constant review.”
The PM urged people to be careful and to get their booster jab as soon as possible.
"We are looking at all kinds of things to keep Omicron under control and we will rule nothing out," he said.
“But at the moment what I think we want people to focus on is exercising caution so ventilation, masks in the appropriate places, all the usual stuff about washing hands, but remember how contagious Omicron really is.
“I think what you’re seeing already is the British public understanding that and you can see in people’s patterns of behaviour since we went to Plan B that they are changing the way they go about their lives, they are changing some of the assumptions they make about the things that they want to do.”
He said scientists were looking at the data “hour by hour”.
“Unfortunately I must say to people that we will have to reserve the possibility of taking further action to protect the public, to protect public health, to protect our NHS,” he said.
“We won’t hesitate to take action.”
Infections reached an all-time high on December 17 with 93,045 infections logged - and today's daily tally is way up on last Monday when 54,661 cases were recorded.
The UK Health Security Agency today confirmed a further 8,044 Omicron cases in the UK.
The Prime Minister was also pressed on a bailout package for the hospitality industry as pubs and restaurants lose trade.
He said “in many ways I regret” the impact on hospitality of Plan B and people socialising less, but added: “If it can help to get down the R (rate of infection), get down the way the disease is multiplying, that can be very helpful to us and the country.
“But what really matters is for everybody to get vaccinated and get boosted above all because the booster really does give you a very high level of protection.”
