The PM said the data is "under constant review", with the situation "extremely difficult" and the "arguments either way are very, very finely balanced" as Omicron cases surge across the country, with hospital admissions spiking in London.

After a lengthy unscheduled cabinet meeting, Mr Johnson said: "Unfortunately, we will have to reserve the possibility of taking further action to protect the public, public health and our NHS."

He added that ministers are not imposing any further restrictions yet but are looking at "all kinds of things to keep Omicron under control and we will rule nothing out".

Mr Johnson also urged the British public to continue to "exercise caution" - such as ventilation, wearing a mask and washing hands - and "get a booster".

"There are still some things that we need to be clearer about before we decide to go further," the PM added.

He said millions of people still have not had their first vaccine, adding: "It makes such a difference, the evidence is overwhelming, it's such a positive thing to do.

"Those who are unvaccinated, whether out of apathy, for whatever reason, please think of this as a great thing to do for you and your family."

Pubs, restaurants and theatres have reported a plethora of cancellations during their busiest period since the government announced England was going into Plan B restrictions and Chief Medical Officer Professor Chris Whitty said people should prioritise who they see ahead of Christmas.

But Mr Johnson did not announce any further financial support for hospitality, instead saying he understood "how tough it must be" but there is help in the form of business rate and VAT relief and funds from local councils.

"We'll keep the economic side of this under review as well," he said.

In Scotland, First Minister Nicola Sturgeon said there will be no changes to measures before Christmas after last week telling the public to limit socialising to just three households ahead of and after the festive period.

She said: "The cabinet will discuss tomorrow and I will set out in parliament if there are any additional or wider steps necessary, but I want to be clear to individuals that the advice I gave out last week is the advice that will take us through Christmas."

Tory MP Dehenna Davison said "we really need some certainty" as she said pubs and restaurants have contacted her over the past two days asking if they should place food and drinks orders, while constituents have asked if they need to postpone their wedding "for the fifth time" or if they can see their mum at Christmas.

The Times reported that Mr Johnson and his cabinet ministers had been considering banning indoor mixing during a two-week circuit breaker but decided the data did not support this move.

Senior ministers have demanded more time to examine the latest Omicron data before making changes, The Sun reported.

Downing Street denied it was an emergency meeting after the government's Scientific Advisory Group for Emergencies (SAGE) warned daily hospital admissions could reach 3,000 without further restrictions.

But they did not deny reports a number of ministers, including Chancellor Rishi Sunak, are against imposing stricter measures without more evidence of the virus' impact.

Former Tory cabinet minister Esther McVey tweeted she is "pleased" the cabinet and PM are "now listening to their backbench MPs and for once pushed back on the scaremongering by the lockdown fanatics".

"It seems the 100-strong backbench rebellion last week has made a difference," she added.

But Labour's shadow health minister, Wes Streeting, said Mr Johnson had "put his party before the public" because he is "too weak to stand up to his own backbenchers, many of whom have no plan beyond 'let the virus rip'".

Earlier on Monday, Deputy Prime Minister Dominic Raab told Sky News he could not make "hard, fast guarantees" that more restrictions would not be imposed ahead of Christmas.

He added he did not anticipate parliament being recalled to vote on new restrictions before Christmas.