The Prime Minister is believed to be considering measures including guidance to work from home and the introduction of domestic vaccine passports for events and large venues.
Downing Street sources insisted “no decisions have been made” but there is widespread speculation that further measures could be imminent.
The Cabinet’s Covid-19 operations (Covid-O) committee is expected to meet on Wednesday to consider the next steps.
One reason for the rapid shift towards Plan B could be figures from the Scientific Advisory Group for Emergencies (Sage) panel which suggested at least 1,000 people a day could need hospital treatment for Omicron by the end of the year without restrictions.
Leaked minutes of a Sage meeting held on Tuesday said the Government should “urgently” consider the need for measures to reduce transmission of the virus and protect the NHS from “unsustainable pressure”, the BBC reported.
The peak of the Omicron wave is “highly likely to be higher” than 1,000 to 2,000 variant- related admissions per day without new rules, the document said.
But the timing is being viewed in suspicion in Westminster, coming as the Prime Minister was forced to apologise after footage emerged of senior aides joking about a Downing Street Christmas party during last December’s lockdown.
At Prime Minister’s Questions, senior Tory William Wragg challenged Mr Johnson about reports that a Cabinet meeting and press conference were planned “to initiate Covid winter Plan B”.
The chairman of the Commons Public Administration and Constitutional Affairs Committee told the Prime Minister: “Very few will be convinced by this diversionary tactic.”
The Prime Minister told him: “No decisions will be taken without consulting the Cabinet.”
The UK Health Security Agency said 568 cases of Omicron have been confirmed, up 131 since Tuesday’s figure.
#OmicronVariant latest information
131 additional confirmed cases of the #Omicron variant of COVID-19 have been reported across the UK.
The total number of confirmed COVID-19 Omicron cases in the UK is 568. pic.twitter.com/5efeE07Gxx
— UK Health Security Agency (@UKHSA) December 8, 2021
A prominent member of the Scientific Advisory Group for Emergencies (Sage) warned that a full UK-wide lockdown to deal with the threat of the Omicron variant cannot be ruled out, although the current threat posed by the strain remains unclear.
The Government has so far insisted it is not time to activate its Plan B – the restrictions that would be brought in to prevent the NHS being overwhelmed this winter.
But Omicron may have changed those calculations in Downing Street, with Mr Johnson telling the Cabinet on Tuesday that “early indications were that it was more transmissible” than the Delta strain.
Restrictions could play a role in slowing the spread of the variant in order to allow more time for the booster jab vaccination campaign to progress.
Sage member Professor Neil Ferguson, from Imperial College London, whose data was instrumental to the UK going into lockdown in March 2020, said the variant is concerning but it is still unknown what its impact will be on severe disease.
He suggested people may be told to work from home in the near future as Omicron is spreading fast, with the variant set to take over from the Delta strain before Christmas.
Speaking in a personal capacity, he told BBC Radio 4’s Today programme: “Certainly case numbers of Omicron are doubling at least every three days, maybe even every two days at the moment, so it’s accelerating very fast and, (to) put that in context, it’s the same if not faster than we saw with the original strain of the virus in March of last year. So it is a concern.
“It’s likely to overtake Delta before Christmas at this rate – precisely when is hard to say.
“We’ll start seeing an impact on overall case numbers – it’s still probably only 2%, 3% of all cases so it’s kind of swamped, but within a week or two, we’ll start seeing overall case numbers accelerate quite markedly as well.”
Prof Ferguson said the peak of this wave of infection will be in January if no measures are taken to slow it down.
Asked whether people should be told to work from home, he said: “There is a rationale, just epidemiologically, to try and slow this down, to buy us more time principally to get boosters into people’s arms, because we do think people who are boosted will have the best level of protection possible, but also to buy us more time to really better characterise the threat.
“So, if you imagine a kind of Plan B Plus with working from home might slow it down – it wouldn’t stop it, but it could slow it down, so it’s doubling rather than every two or three days, every five or six days.”
At Prime Minister’s Questions, Mr Johnson apologised after footage emerged of his then spokeswoman Allegra Stratton joking about a December 2020 party at a mock press conference just days after the alleged event.
He ordered an investigation by Cabinet Secretary Simon Case “to establish all the facts and to report back as soon as possible – and it goes without saying that if those rules were broken then there will be disciplinary action for all those involved”.
But he insisted again that he had been “repeatedly assured since these allegations emerged that there was no party and that no Covid rules were broken”.