At a press conference on Wednesday, the chief medical officer warned that [pandemic] records will be broken a lot over the next few weeks" and warned of "two epidemics" from Delta and Omicron.
“What we’ve got is two epidemics on top of one another – an existing Delta epidemic, roughly flat, and a very rapidly-growing Omicron epidemic on top of it," he said.
When asked about Christmas festivities in the run up to Christmas, Whitty urged caution and said the public needed to “prioritise what matters” and “deprioritise other things”.
"[You] don’t need a medical degree to realise that is a sensible thing to do with an incredibly infectious virus," he said.
Boris Johnson said he agreed with much of what Whitty said, but said people should not cancel Christmas plans, but also said the public should "think carefully" about whether they should go.
However earlier on Wednesday, Number 10 said guidance remained the same on Christmas parities - that they should continue and not cancel - but urged people to take lateral flow tests before.
At the press conference, Johnson also repeated his calls for the public to get their booster jabs describing them as “absolutely vital”.
“The wave on Omicron continues to roll in across the whole of the United Kingdom,” he said.
Adding: “I’m afraid we’re also seeing the inevitable increase in hospitalisations up by 10% nationally, week on week, and up by almost a third in London.”
He stressed booster jabs was one of the key ways to prevent Omicron overwhelming the NHS.
It comes as the group of Independent SAGE scientists called for an immediate "circuit breaker" to stem the surge of the new variant.
"Omicron is doubling so fast that sheer numbers will v likely outweigh any advantage of reduced severity (if it exists)," said Professor Christina Pagel from Independent SAGE on Twitter.
"To prevent NHS being overwhelmed in a few weeks & for a safer Xmas we need to act now. Not next week, not after Xmas, now.
"We are calling for an immediate *10 day* circuit break to protect NHS & enable safer mixing over Xmas (25-28 December).
"Reassess over Xmas to see what is needed then, when much more info available. Situation changing so fast, can't plan far ahead."
The UK recorded its highest ever number of COVID cases in a 24 hour period 78,610 new cases reported.
It was also one of the highest ever days for jabs with 656,711 booster vaccinations recorded in a 24 hour period.
Watch: COVID-19: Omicron will cause 'significant increase' in hospital admissions, Professor Chris Whitty warns